Many phenomena and experiments spend in the face of an educational institution very difficult or impossible. On the plot of the Sun car moved evenly to the body located in the elevator experienced a reboot

13.07.2020

How to replace the dough for domestic test

Mel rock, description, properties, deposits and photos

How many days start?

When and how the earth's message was formed as the earth appeared

On the plot de car moved equally, the acceleration vector is directed opposite to the velocity vector

On the AB plot, the car moved uniformly

The acceleration module on the AB section is less than the acceleration module on the section DE.

Three bodies of the same mass of 3 kg each made movement. The relocation projection equations are presented in the table. What schedule is the dependence of the projection of force on the time acting on each body?

Decide the task.

9. The body suspended to the cable weighing 10kg rises vertically. What acceleration is the body moving if the cable is the rigidity of 59kn / m lens by 2 mm? What is the force of elasticity that occurs in the cable?

Dano: C: Solution:

10. The average satellite height over the ground surface is 1700 km. Determine the speed of its movement.

Dano: C: Solution:

Decide the task.

A truck weighing 5 kg moves under the action of a weight of 2 kg. Determine the tension of the thread if the friction coefficient is 0.1.

Danar: Solution:

Option 2.

1. The following lists the movements of the bodies relative to the Earth. What is the reference system associated with one of these bodies, cannot be considered inertial? The reference system associated with the Earth is to be inertial.

1) The girl runs at a constant speed

2) The car moves uniformly horizontal part of the road

3) The train moves equally

4) Hockey washer evenly slides smooth ice

2. On the body weighing 2 kg there are four forces. What is equal to the acceleration of the body, if

F 1 \u003d 20 H, F 2 \u003d 18 H, F 3 \u003d 20 H, F 4 \u003d 16 N.

1) 2 m / s 2 2) 4 m / s 2 3) 1 m / s 2 4) 8 m / s 2

3. What expression determines the value of the first satellite space rate if the radius of its circular orbit R, and the acceleration of the free fall at this height g?

4. In order for the body in the elevator to experience overload (weight increase), it is necessary:

1) accelerated elevator movement up 2) Slow motion elevator up 3) Accelerated elevator movement down 4) This state is impossible

5. The man was driving two identical children on the sleds along the horizontal road. Then one child got up from Sanok, but the man continued to move at the same constant speed. How did the friction force change?

1) did not change 2) increased by 2 times 3) decreased by 2 times 4) increased by 50%

6. On the inclined plane is uniformly up the bar moves. What vector shown in the picture is excess or wrong?

7. Car speed module Weighing 1000kg varies in accordance with the schedule shown in the figure. What approval is true?

2) On the CD plot, the car moved equally, the acceleration vector coincides in direction with a velocity vector

3) On the section de car moved equally, the acceleration vector coincides in direction with a velocity vector

4) The acceleration module on the AB site is less than the acceleration module on the section DE

7. Using the condition of the task, set the correspondence of the equations from the left column of the table with their graphs in the right column.

Three bodies of the same mass of 2 kg each made movement. The relocation projection equations are presented in the table. What schedule is the dependence of the projection of force on the time acting on each body?

Decide the task.

8. The bus weighing 15 t is rotated from the place with an acceleration of 0.7 m / s 2. What kind of friction is valid for the bus if the engine of the engine thrust is 15 kN? Answer to express in the book. What equal to the coefficient friction?

Dano: C: Solution:

9. The average satellite height over the surface of the Earth is 900 km. Determine the speed of its movement.

Dano: C: Solution:

Decide the task.

10. Two shipments with the masses of 200 g and 300 g are connected by thread. Determine the acceleration of goods and the strength of the thread tension between them if the power of T 1 was attached to the body of T 1, directed horizontally to the right.

Dano: C: Solution:

Evaluation _____ Signature of the teacher ________________ / hp Tishkin /

Option 3.

Part and select one right answer.

1. Parachutist lowers vertically with a constant speed of 2 m / s. The reference system associated with the Earth is to be inertial. In this case:

1) There are no forces on the parachute

2) The strength of gravity is equalized by the force of Archimedes acting on the parachute

3) the sum of all forces acting on the parachute is zero

4) the sum of all forces is constant and not equal to zero

2. On the body weighing 2 kg, the forces 3 N and 4 N, directed perpendicular to each other. What is the acceleration of the body?

1) 3.5 m / s 2 2) 2.5 m / s 2 3) 7 m / s 2 4) 10 m / s 2

3. The satellite mass M moves around the planet over a circular orbit of Radius R. Mass of the planet M. What expression determines the value of the acceleration of the satellite movement?

4. The elevator has spring scales on which a person stands. How to change the scales when accelerated motion elevator up and down?

1) up - will increase, down - decrease

2) Up - decrease, down - will increase

3) up - will increase, down - do not change

4) Up - do not change, down - will increase

5. The man is carrying a child on the sleds along the horizontal road. Then the second is the same child in Sanki, but the person continued to move at the same constant speed. How has the friction coefficient changed?

1) did not change 2) increased by 2 times 3) decreased by 2 times 4) increased by 50%

6. On the inclined plane, the bar moves the bar. What vector shown in the picture is excess or wrong?

7. The velocity velocity module weighing 1000 kg changes in accordance with the schedule shown in the figure. What approval is true?

1) on the site Sun car moved equally

2) On the CD plot, the car moved equally, the acceleration vector is directed oppositely the velocity vector.

3) on the EF plot rested

4) The acceleration module on the AB site is less than the acceleration module on the section DE

8. Using the condition of the task, set the correspondence of the equations from the left column of the table with their graphs in the right column.

Three bodies of the same mass of 4 kg each made movement. The relocation projection equations are presented in the table. What schedule is the dependence of the projection of force on the time acting on each body?

Decide the task.

9. The elevator is lowered with an acceleration of 2 m / s 2. In the elevator on the spring, the rigidity of 560 n / m hangs a weight of 0.7 kg. What is the power of elastic springs? How long the spring lengthened?

Danar: Solution:

10. The average satellite height over the ground is 600 km. Determine the speed of its movement.

Dano: C: Solution:

Decide the task.

11. The bar mass of 400 g comes into motion with an acceleration of 0.4 m / s 2 under the action of cargo weighing 100 g. Find the force of friction and the friction coefficient of Bruck about the surface.

Dano: C: Solution:

Evaluation _____ Signature of the teacher ________________ / hp Tishkin /

Option 4.

Part A. Choose one right answer

1) Lift freely drops 2) Elevator rises evenly

3) The elevator moves slowly up 4) The elevator moves accelerated down

2. On the body weighing 2 kg there are four forces. What is equal to the acceleration of the body, if F 1 \u003d 12 H, F 2 \u003d 18 H, F 3 \u003d 20 H, F 4 \u003d 18 N.

1) 6 m / s 2 2) 16 m / s 2 3) 2 m / s 2 4) 4 m / s 2

3. The mass of the moon is about 81 times less than the mass of the Earth. What is equal to the relationship of the power of the World F 1, acting from the ground to the moon, to the force of F 2, acting from the moon to the Earth?

1) 1/81 2) 81 3) 9 4) 1

4. How to make a weight of 10n stretch the spring of a dynamometer with force, greater than 10n?

1) Move the dynamometer with the guy down with some acceleration

2) Move the dynamometer with the Gary up with some acceleration

3) Dynamometer with Gary must fall freely

4) this is impossible to implement

5. The man was driving two identical children on the sleds along the horizontal road. Then one child got up from Sanok, but the man continued to move at the same constant speed. As has changed
coefficient of friction?

1) increased by 2 times 2) decreased by 2 times 3) increased by 50% 4) did not change

6. On the inclined plane still lies the bar. What vector shown in the picture is excess or wrong?

1) 2) 3) 4)

7. The velocity velocity module weighing 1000 kg changes in accordance with the schedule shown in the figure. What approval is true?

1) On the CD plot, the car moved equally, the acceleration vector coincides in the direction with the velocity vector

2) the acceleration module on the AD plot is larger than the acceleration module on the section DE

3) On the section de car moved equally, the acceleration vector is directed opposite to the velocity vector

4) On the AB plot, the car moved uniformly

8. Using the condition of the task, set the correspondence of the equations from the left column of the table with their graphs in the right column.

Decide the task.

9. The car weighing 1 t is moving with an acceleration of 0.8 m / s 2. Friction force 2 kN acts on the car. Determine the power of the engine thrust (express the answer to the KN) and the friction coefficient.

Dano: C: Solution:

10. The average satellite height over the surface of the Earth is 300 km. Determine the speed of its movement.

Dano: C: Solution:

Decide the task.

11. On the cord, overlaid through the stationary block, are suspended with two shipments with the masses of 200 g and 300 g. What acceleration moves loads? What is the thread tension force?

Dano: C: Solution:

Evaluation _____ Signature of the teacher ________________ / hp Tishkin /

Date "___" _________ 20 ____

Task 12 on the topic

"Application of the law of preservation of body pulse"

Task Share:

1. Invite the pulse of the truck weighing 10 ton, moving at a speed of 36 km / h, and a passenger car weighing 1 ton, moving at a speed of 25 m / s.

Dano: C: Solution:

2. The train weighing 2000 ton, moving straightly, helped the speed from 36 to 72 km / h. Find a change in the pulse.

Danar: SI: Solution: Dano: C: Solution:

Dano: C: Solution:

Evaluation _____ Signature of the teacher ________________ / hp Tishkin /

Date "___" _________ 20 ____

Task 15 on the topic

"Education and spread of waves.

Option 1.

The plane flies in a straight line at a constant speed at an altitude of 9 km. The reference system associated with the Earth is to be inertial. In this case:

1) no forces act on the plane

2) the plane does not work in gravity

3) the sum of all the forces acting on the plane is zero

4) gravity is equal to the power of Archimedes acting on the plane

On the body weighing 1 kg, 6 N and 8H strength are acting, directed perpendicular to each other. What is the acceleration of the body?

1) 2 m / s 2 2) 5 m / s 2 3) 10 m / s 2 4) 14 m / s 2

Satellite masst. R.

1) 2) 3) 4)

To the spring is 10 cm long, the coefficient of the stiffness of which is 500 N / m, joined the load weighing 2 kg. What was the length of the spring?

1) 12 cm 2) 13 cm 3) 14 cm 4) 15 cm

The man was carrying a child on the sleds along the horizontal road. Then the second is the same child in Sanki, but the person continued with the same constant speed. How did the friction force change?

On the inclined plane slides the bar slides. What vector shown in the picture is excess or wrong?

1) 2) 3) 4)

2) on the plotDE.

3) on the section AB car moved uniformly

DE.

Part B.

Decide the task.

Body suspended to the cable weighing 10 kg rises vertically. What acceleration is the body moving if the cable with rigidity of 59 kN / m lens by 2 mm? What is the force of elasticity that occurs in the cable?

The average satellite height above the ground is 1700 km. Determine the speed of its movement.

Option2 .

Part A Select one correct answer.

Below are the movements of the bodies relative to the Earth. What is the reference system associated with one of these bodies, cannot be considered inertial? The reference system associated with the Earth is to be inertial.

1) The girl runs at a constant speed

2) The car moves uniformly horizontal part of the road

3) The train moves equally

4) Hockey washer evenly slides on smooth ice

1) 2 m / s 2 2) 4 m / s 2 3) 1 m / s 2 4) 8 m / s 2

What expression determines the value of the first satellite space rate if the radius of the circular orbitR., and speeding free fall at this heightg.?

1) 2) 3) 4)

So that the body in the elevator has experienced overload (weight gain) is necessary:

1) accelerated elevator movement up

2) slow motion elevator

3) accelerated elevator movement down

4) this state is impossible

The man was driving two identical children on the sleds along the horizontal road. Then one child got up from the sled, but the person continued to move with the same constant speed. How did the friction force change?

1) not changed 2) increased by 2 times

3) decreased by 2 times 4) increased by 50%

1) 2) 3) 4)

The velocity module weighing 1000 kg changes in accordance with the schedule shown in the figure. What approval is true?

1) on the site Sun car moved equally

2) on the plot withD.

3) on the plotDE. The car moved equally, the acceleration vector coincides in direction with a velocity vector.

4) The acceleration module on the AB site is less than the acceleration module on the siteDE.

Part B.

Using the condition of the problem, set the correspondence of the equations from the left column with their graphs in the right column.

Decide the task.

The bus weighing 15 t is risted from the place with an acceleration of 0.7 m / s 2 . What kind of friction is valid for the bus if the power of the engine is 15 kN? Answer to express in the book. What is the coefficient of friction?

The average satellite height over the surface of the Earth is 900 km. Determine the speed of its movement.

Option 3.

Part A Select one correct answer.

The parachutist descends vertically with a constant speed of 2 m / s. The reference system associated with the Earth is to be inertial. In this case:

1) There are no forces on the parachute

2) The strength of gravity is equalized by the force of Archimedes acting on the parachute

3) the sum of all forces acting on the parachute is zero

4) the sum of all forces is constant and not equal to zero

On the body weighing 2 kg, the forces 3 N and 4 N, directed perpendicular to each other. What is the acceleration of the body?

1) 3.5 m / s 2 2) 2.5 m / s 2 3) 7 m / s 2 4) 10 m / s 2

Satellite masst. moving around the planet over a circular orbit of radiusR.. Mass of the planet M. What expression determines the value of the speed of the satellite?

1) 2) 3) 4)

The elevator has spring scales on which a person stands. How will the testimony of weights change with an accelerated elevator movement up and down?

1) up - will increase, down - decrease

2) Up - decrease, down - will increase

3) up - will increase, down - do not change

4) Up - do not change, down - will increase

The man was carrying a child on the sleds along the horizontal road. Then the second is the same child in Sanki, but the person continued with the same constant speed. How has the friction coefficient changed?

1) not changed 2) increased by 2 times

3) decreased by 2 times 4) increased by 50%

On the inclined plane, the bar moves the bar equally upwards. What vector shown in the picture is excess or wrong?

1) 2) 3) 4)

The velocity module weighing 1000 kg changes in accordance with the schedule shown in the figure. What approval is true?

1) on the plot of the Sun car moved evenly

2) on the plot withD. The car moved equally, the acceleration vector is directed opposite to the velocity vector

3) on the plotEF. The car was resting

4) The acceleration module on the AB site is less than the acceleration module on the siteDE.

Part B.

Using the condition of the problem, set the correspondence of the equations from the left column with their graphs in the right column.

Decide the task.

The elevator is lowered with acceleration 2 m / s 2 . In the elevator on the spring, the rigidity of 560 n / m hangs a weight of 0.7 kg. What is the power of elastic springs? How long the spring lengthened?

The average height of the satellite above the ground is 600 km. Determine the speed of its movement.

Option4 .

Part A Select one correct answer.

1) Lift freely falls

2) Elevator rises evenly

3) The elevator moves slowly up

4) The elevator moves accelerated down

On the body weighing 2 kg there are four forces. What is equal to the acceleration of the body, ifF. 1 =12 H., F. 2 =18 H., F. 3 =20 H., F. 4 =18 H..

1) 6 m / s 2 2) 16 m / s 2 3) 2 m / s 2 4) 4 m / s 2

The mass of the moon is about 81 times less than the mass of the Earth. What is equal to the relation of the power of the worldF. 1 acting from the ground to the moon, to strengthF. 2 acting from the moon to Earth?

1)1/81 2) 81 3) 9 4) 1

How to make a weight of 10 H stretch the spring of a dynamometer with force, greater than 10 n?

1) Move the dynamometer with the guy down with some acceleration

2) Move the dynamometer with the Gary up with some acceleration

3) Dynamometer with Gary must fall freely

4) this is impossible to implement

1) increased by 2 times 2) decreased by 2 times

3) increased by 50% 4) has not changed

On the inclined plane evenly up the barbed bar. What vector shown in the picture is excess or wrong?

1) 2) 3) 4)

The velocity module weighing 1000 kg changes in accordance with the schedule shown in the figure. What approval is true?

1) on the plot withD. The car moved equally, the acceleration vector coincides in direction with a velocity vector

2) The acceleration module on the AV region is larger than the acceleration module on the siteDE.

3) on the plotDE. The car moved equally, the acceleration vector is directed opposite to the velocity vector.

4) on the section AB car moved evenly

Part B.

Using the condition of the problem, set the correspondence of the equations from the left column with their graphs in the right column.

Decide the task.

The car weighing 1 t is moving with acceleration 0.8 m / s 2 . The car is the power of 2 kN? Determine the power of the engine thrust (express the answer to the KN) and the friction coefficient.

The average satellite height over the surface of the Earth is 300 km. Determine the speed of its movement.

Examination number 2.

Dynamics.

DEMO VERSION

A1. The plane flies in a straight line at a constant speed at an altitude of 9 km. The reference system associated with the Earth is to be inertial. In this case:

1. There are no strength on the plane

2. The air force does not work as a plane

3. The sum of all forces acting on the plane is zero

4. The strength of gravity is equal to the power of Archimedes acting on the plane

A2.On the body weighing 2 kg there are four forces. What is equal to the acceleration of the body, if

F 1 \u003d 20 H, F 2 \u003d 18 H, F 3 \u003d 20 H, F 4 \u003d 16 H

A3.The satellite mass M moves around the planet over a circular orbit of Radius R. Mass of the planet M. What expression determines the value of the satellite movement?

A4.So that the body in the elevator has experienced overload (weight gain) is necessary:

accelerated elevator movement up

slow motion elevator up

accelerated elevator movement down

such a state is impossible

A5.The man was carrying a child on the sleds along the horizontal road, then in Sledge, the second is the same child, but the person continued to move at the same constant speed, as the friction force changed?

not changed

increased by 2 times

decreased by 2 times

increased by 50%

A6.On the inclined plane, the bar is moving uniformly. What vector shown in the picture is excess or wrong?

A7.The velocity module weighing 1000 kg changes in accordance with the schedule shown in the figure. What approval is true?

1. On the plot of the Sun car moved uniformly

2. On the section DE the car moved equal to the background, the speed of the acceleration is directed opposite to the velocity vector

3. On the car, the car moved evenly

4. The acceleration module on the AB section is less than the acceleration module on the section DE

IN 1. Three bodies of the same mass of 2 kg each performed movement. The relocation projection equations are presented in the table. What schedule is the dependence of the projection of force on the time acting on each body?

AT 2.Body suspended to the cable weighing 10 kg rises vertically. What acceleration is the body moving if the cable with rigidity of 59 kN / m lens by 2 mm?

IN 3.The average satellite height over the surface of the Earth is 900 km. Determine the speed of its movement. (Answer in km / s)

Task number 6.

Question:

Two forces were applied to the body, the modules of which are 10 H and 20 N. It is known that the forces are directed on one direct and in opposite sides. What will be the resultant force (in H)?

Write down the number:

________10 ________________

Task number 7.

Question:

On the body weighing 100 kg there is an equal force equal to 20 N. What is the body acceleration module (in m / s 2)?

Write down the number:

_________0,2 _______________

Task number 8.

Question:

The body weighing 5 kg rests on the horizontal surface of the table. Determine what force (in H) the table will act on this body?

Write down the number:

__________49 _______________

Task number 9.

Question:

The figure shows two forces acting on the body. Find the power module F 2. (in H) if the body moves to the right with a constant speed of 2 m / s.

Picture:

Write down the number:

________17,3 ________________

Task number 10.

Question:

The body M is moving with an acceleration of 3 m / s 2. How many times should the resulting force increase so that the body began to move with an acceleration of 9 m / s 2?

Write down the number:

______3_________________

The law of global gravity. Space speeds

Task number 1

Question:

The coefficient of proportionality in the formula describing the law of world community is numerically equal to ...

1) about 10 9

2) about 10 5

3) about 10 -19

4) about 10 -11

Task number 2.

Question:

Choose the values \u200b\u200bon which the first two space speeds of this planet depend

Select a few out of 5 answer options:

Weight

2) Albedo.

Radius

4) the period of appeal around its axis

5) the period of appeal around his star

Task number 3.

Question:

Choose true allegations

__ Gravitational interaction between bodies is always manifested in the form of mutual attraction

__ The force of gravity is proportional to the masses of bodies

The force of gravity is inversely proportional to the distance between the bodies.

The law of world community is universal and can be applied with high accuracy to any pair of bodies.

Task number 4.

Question:

The speed with which the body should move to leave the orbit of this celestial body - this is ...

Select one of 4 answer options:

1) The first cosmic velocity of this body

2) the second cosmic velocity of this body

Third Space Speed \u200b\u200bof this Body

4) Fourth Space Speed \u200b\u200bof this Body

Task number 5.

Question:

Pencil rests on the table. What interaction is this due?

Select one of 4 answer options:

Gravitational

2) electromagnetic

3) strong

Task number 6.

Question:

Find strength (in MN), which is attracted by two asteroids in open space weighing 10,000 tons each, if the distance between them is 1 km away.

Write down the number:

_______6,67 _________________

Task number 7.

Question:

In order to make an aircraft with an artificial satellite of some planet, this aircraft, flying from this planet you need to develop a speed of 2 km / s. If the mass of this planet is 10 23 kg, then what is its radius (in km)?

Write down the number:

______1667,5 _________________

Task№8.

Question:

Find the second cosmic speed of the moon in km / s. The mass of the moon is 7.3x10 22 kg, but a radius - 1737 km.

Write down the number:

______1,67 _________________

Task number 9.

Question:

Find strength (in TN), with which the sun acts on Pluto. The mass of the sun is 2x10 30 kg, pluton mass - 1.3x10 22 kg. The average distance between the Sun and Pluto to take equal to 5913 million km.

Write down the number:

_____49600 _________________

Task number 10.

Question:

Find the radius of the planet (in km), the first cosmic speed of which is 12 km / s, and the acceleration of the free inclination is 15 m / s 2.

Write down the number:9600

Gravity. Weight, weightlessness, overload

Task number 1

Question:

Choose true allegations

Specify the truth or false answer options:

Yes) The strength of gravity acting on the body is equal to the product of body weight and acceleration of free fall

No) body weight is equal to the product of body weight and acceleration of free fall

No) Weight is a scalar value.

Yes) Weight is the force acting on the support or suspension

Task number 2.

Question:

A person experiences overload while in the elevator, if ...

Select one of 4 answer options:

1) Lift rests

Elevator rises up

3) The elevator is lowered down

4) if a person stands on his hands

Task number 3.

Question:

Cosmonauts in the near-earth orbit are experiencing a state of weightlessness, because ...

1) they are far enough from the ground so that the strength of gravity ceases to

They are in a free fall, falling around the earth

3) they are starting to attract other heavenly bodies, and the total effect of these bodies balance the gravity force acting from the ground

Task number 4.

Question:

Configure the situation with the consequence of this situation.

Specify the correspondence for all 4 answer options:

The pilot experiences overload

2) The power of gravity acting on the pilot is not equal to its weight

3) The strength of gravity acting on the pilot is equal to its weight

4) the pilot is experiencing weightlessness

4) the plane goes into the corkscrew

The plane comes out of the peak

3) The plane flies with horizontal acceleration

2) The plane flies with vertical acceleration

Task number 5.

Question:

Is land in a state of weightlessness?

Select one of 3 answers:

3) depending on the selection of the reference system

Task number 6.

Question:

The waiter raises a tray vertically up with an acceleration of 3 m / s 2. The mass of the dishes lying on the tray is 2 kg. Determine the strength (in H), with which the dishes acts on the tray.

Write down the number:

____________26 _______________

Task number 7.

Question:

On the board resting the bar weighing 400 g. The board raise together with Bru and let go. Find strength (in H) with which the bar will act on the board during the flight.

Write down the number:

_______0 ________________

Task number 8.

Question:

A man weighing 50 kg swings on a swing that is attached using two identical ropes. The length of each rope is 2 m. The weight of a person at the moment when he passes the lower point of the trajectory of his movement, is 1.2 kN. Find the maximum linear speed (in m / s), with which a person swings.

Write down the number:

_______5,29 ___________________

Task number 9.

Question:

The car moves through the bridge. At the same time, its weight decreases. Then this bridge ...

Select one of 4 answer options:

2) deployed down

Deposited up

4) not enough information to make any conclusions

Task number 10.

Question:

The elevator moves up at a speed of 1 m / s. In the elevator there is a load weighing 100 kg. What force (in n) does this cargo act on the elevator during such a movement?

Write down the number: 981

1. As you already know, the strength with which the body, due to its attraction to the Earth, acts on the support or suspension, is called weight body P..

Body weight is applied to the support or suspension; Unlike him, gravity is applied to the body. Weight and gravity strength have not only different points of the application, but also different nature: the power of gravity - gravitational force, and the weight is the power of elasticity.

From the course of the 7th Class Physics, you also know that if the body, suspended on the thread or placed on the support, rests or moves evenly and straightly, then its weight in the module is equal to the power of gravity:

P. = mG..

2. Suppose now that the body together with the support or suspension moves relative to the ground with acceleration. Will there be a body weight and gravity?

Consider the movement of a person in the elevator. Let the elevator have acceleration a.directed down (Fig. 52). In the inertial reference system associated with the Earth, the person acts: the strength of gravity, directional, and the power of elasticity from the floor of the elevator, directed upwards. The power of elasticity in this case is called power reaction support And denote the letter N.. The equitive of these forces informs a person acceleration.

Using the second law of Newton, you can write in vector form:

F. = mA.,
F. litter +. N. = mA..

We direct the axis Y. vertically down and write this equation in projections on this axis, given that F. litter \u003d. mG., projections acceleration and gravity on the axis Y. Positive, and the projection of the reaction force support is negative. We get:

mG. – N \u003d MA..

From here:

N. = mG. – mA. = m.(g. – a.).

According to the third law of Newton, the body weight of the module is equal to the power of the reaction of the support:

P. = N..

Then

P. = m.(g. – a.).

From the resulting formula, it can be seen that body weight is less gravity. In this way, if the body together with a support or suspension moves down to the acceleration, which is directed in the same way as the acceleration of the free fall, then its weight is less than the force of gravity, i.e. less weight of the resting body.

We have a decrease in weight you are experiencing, being in the elevator, at the time of starting its movement down.

If the acceleration of the body is equal to the acceleration of free fall a. = g., then body weight P. \u003d 0. This condition is called condition. justice. In a state of weightlessness, astronauts are in a spacecraft during the flight, as they move around the ground with centripetal acceleration equal to the acceleration of free fall.

But not only astronauts experience the state of weightlessness. In such a state, the runner can be in short periods when both legs are torn off from the ground; Jumper from a springboard during the flight.

3. Consider the movement of the elevator and the person standing in it. But only now the elevator has acceleration. a.awarded up (Fig. 53).

Using the second Newton law, you can write:

F. = mA.,
F. litter +. N.= mA..

By sending the axis Y. Vertically down, write this equation in projections for this axis:

mG. – N \u003d -MA; N. = mG. + mA.; N. = m.(g. + a.).

Insofar as P. = N.T.

P. = m.(g. + a.).

From the formula it is clear that the weight in this case is more gravity. In this way, if the body, together with a support or suspension, moves with an acceleration directed opposite to speeding up the free fall, then its weight is greater than the strength of gravity, i.e. more weight of the resting body.

An increase in body weight caused by the movement with acceleration is called overload.

You are overloaded in the elevator, at the time of starting its movement upwards. Huge overloads are experiencing astronauts and pilots of jet aircraft during takeoff and landing; Pilots performing on the plane shape of the highest pilot "Dead loop" at its lower point. In order to reduce the pressure on the skeleton of astronauts during take-off, special chairs are made in which astronauts are in a half-hour position. At the same time, the pressure force that acts on the astronaut is distributed on the B € a large area, and the pressure on the skeleton becomes less than when the cosmonaut is in a sitting position.

4. An example of solving the problem

What is the weight of the pilot weighing 70 kg, performing a "dead loop", at the bottom and upper points of the trajectory, if the radius of the loop 200 m, and the speed of the aircraft during the passage of the loop 100 m / s?

Dano:

Decision

m. \u003d 70 kg

R. \u003d 200 M.

v. \u003d 100 m / s

g. \u003d 10 m / s 2

At the pilot in the lower and at the top points of the trajectory there are gravity F. heat and power of the armchair N. (Fig. 54). The power reaction force is equal to the pilot weight module: P. = N..

In accordance with the second law of Newton, you can write:

N. + F.heavy \u003d MA..

P.1?

P.2?

For the lower point of the trajectory, this equation in the projections on the axis Y.(Fig. 54, but) Will look at:

–N. 1 + F. litter \u003d - mA., or N. 1 – mG.= mA..

Hence,

P. 1 = N. 1 = mA.+ mG.= m.(a. + g.).

For the top point of the trajectory (Fig. 54, b.) You can write:

N. 1 + F. litter \u003d. mA..

From here

N. 1 = mA. – mG..

Hence,

P. 2 = N. 1 = m.(a. – g.).

Insofar as a. \u003d, T.

P. 1 = m. + g.; P. 2 =– g..

P. 1 \u003d 70 kg + 10 m / s 2 \u003d 4200 H;

P. 2 \u003d 70 kg - 10 m / s 2 \u003d 2800 N.

If the power of gravity acting on the pilot, F. Harry \u003d 70 kg 10 m / s 2 \u003d 700 N, then its weight at the bottom point of the trajectory is 6 times greater than the power of gravity: \u003d\u003d 6. They say that the pilot is experiencing six-time overload.

At the top point of the trajectory, the pilot is experiencing fourfold overload: \u003d\u003d 4.

Answer: P. 1 \u003d 4200 N; P. 2 \u003d 2800 N.

Questions for self-test

1. What is called body weight? What is the nature of body weight?

2. In which case body weight in the module is equal to the strength of gravity?

3. How the body weight changes when it moves with acceleration, directed up; down?

4. What condition is called immobility? When does it come?

5. What condition is called overload? When are overloaded?

Task 15.

1. The elevator begins to move down with the acceleration of 2 m / s 2. What is the weight of 60 kg standing in this elevator?

2. What is the force of a car with a mass of 1 ton, presses on the middle of a convex bridge having a radius of curvature of 30 m? Car speed 72 km / h.

3. The stone weighing 400 g rotate evenly in the vertical plane on the rope with a length of 1 m at a speed of 2 m / s (Fig. 55). What is the rope tension force when the top and bottom point of the trajectory passing?

Many phenomena and experiments spend in the face of an educational institution very difficult or impossible. On the plot of the Sun car moved evenly to the body located in the elevator experienced a reboot

Read also