Introductory test in physics (grade 8). Fall of bodies When a body released from the hands falls,

Introductory control in physics 8kl OPTION No. 2 Complete the sentence with one word: 1. The physical quantity that characterizes the inertia of the body is called ____________________ 2. The force with which the Earth attracts bodies to itself is called ____________________ 3. The force that prevents movement is called _______________________________________ 4. A device for measuring length ____________________ 5. A wheel with a groove fixed in a cage is ___________ 6. A device for measuring pressure _________________ TEST 1. The smallest particles that make up substances are called: a) molecules, b) microparticles, c) grains. 2. Diffusion can be slowed down if: a) cool the body, b) heat it, c) move it from one table to another. 3. What general properties are characteristic of solids: a) they have their own shape and volume, b) they are easily compressed, c) they are practically not compressible. 4. What formula can be used to calculate body volume? a)F=mg. b) p=m:v. d) V=S:t e) V=abc 5. What force makes all bodies fall to the Earth? a) the force of friction, b) the force of elasticity, c) the force of gravity, d) the weight of the body. 6. What formula can be used to calculate gravity? a) F=mg b) F=mgh. d) p=F:S e) V=S:t 7. What is the unit of pressure? a) Pa b) N c) m/s d) kg 8. Which of the astronauts was the first to fly into space? a) Gagarin b) Titov c) Tereshkova d) Leonov. 9. By what formula can work be calculated? a) F=pgh b) A=F S d) N=A:t

10. the body performs mechanical work when a) it moves, b) a force acts on it, c) a force acts on it and it is TESTS IN PHYSICS 8cl. TEST 1 Thermal motion. Temperature. 1. Diffusion occurs faster if a) the movement of molecules slows down b) the movement of molecules stops c) the speed of movement of molecules increases 2. What is the difference between warm water and cold water? a) the speed of movement of molecules b) the structure of molecules c) transparency 3. Which of the phenomena refers to thermal? a) Earth's rotation around the Sun b) rainbow c) snow melting 4. What is the trajectory of gas molecules? a) along a straight line b) along a curvilinear c) along a broken line 5. In what bodies can molecules vibrate, rotate, move relative to each other? a) in gases b) in liquids c) in solids 6. Body temperature is related a) to the kinetic energy of the body b) to the potential energy of the body c) to the average kinetic energy of the molecules

TEST No. 2 Internal energy 1. The kinetic energy of a body depends a) only on the mass of the body b) only on the speed of the body c) on the mass and on the speed of the body the transition of kinetic energy into potential energy c) .kinetic and potential energies do not change 3. The mechanical energy of a piece of plasticine that has fallen to the floor, a) will not change b) will disappear without a trace c) will turn into another form of energy 4. What energy is called the internal energy of the body? a) body movement energy b) interaction energy of body parts c) kinetic and potential energies of body parts bodies relative to other bodies 6. Can a body not have internal energy? a) it can, if the body has a very low temperature b) it can, if the body does not have mechanical energy c) it cannot under any circumstances Literature: SYPCHENKO G.V. PHYSICS tests 8th grade Saratov: Lyceum, 2012.80c Internet resource

Tasks in mechanics (dynamics), on the topic
Movement under the influence of gravity in a vertical direction
From the manual: GDZ to the problem book Rymkevich for grades 10-11 in physics, 10th edition, 2006

Find the acceleration of free fall of the ball according to figure 31, made from a stroboscopic photograph. The interval between shots is 0.1 s, and the side of each square of the grid in the life-size photo is 5 cm
SOLUTION

In free fall, the first body was in flight 2 times longer than the second. Compare the final velocities of bodies and their displacements
SOLUTION

G. Galileo, studying the laws of free fall (1589), threw various objects without initial speed from an inclined tower in the city of Pisa, the height of which is 57.5 m. How long did objects fall from this tower and what was their speed when they hit the ground
SOLUTION

A swimmer, having jumped from a five-meter tower, plunged into the water to a depth of 2 m. How long and with what acceleration did he move in the water
SOLUTION

A body falls freely from a height of 80 m. What is its displacement in the last second of the fall
SOLUTION

How long did the body fall if it traveled 60 m in the last 2 s?
SOLUTION

What is the displacement of a freely falling body in the nth second after the start of the fall
SOLUTION

What initial speed must be given to a stone when it is thrown vertically down from a bridge 20 m high so that it reaches the surface of the water in 1 s? How long would a stone fall from the same height without initial velocity
SOLUTION

One body falls freely from a height h1; simultaneously with it, another body starts moving from a higher height h2. What should be the initial speed u0 of the second body so that both bodies fall at the same time
SOLUTION

An arrow fired from a bow vertically upwards fell to the ground after 6 s. What is the initial speed of the boom and the maximum lifting height
SOLUTION

How many times greater is the height of the body thrown vertically upwards on the Moon than on Earth, with the same initial velocity?
SOLUTION

By how many times must the initial velocity of a body thrown vertically upwards be increased so that the height of the lift is increased by 4 times
SOLUTION

From a point located at a sufficiently high altitude, two bodies are simultaneously thrown with the same modulus of velocities v0 = 2 m/s: one vertically upwards, and the other vertically downwards. What will be the distance between the bodies after 1 s; 5 s; after a period of time equal to
SOLUTION

When throwing the ball vertically upwards, the boy tells him the speed is 1.5 times greater than the girl. How many times higher will the ball thrown by the boy rise
SOLUTION

An anti-aircraft gun projectile fired vertically upwards at a speed of 800 m/s reached its target in 6 s. At what height was the enemy aircraft and what was the speed of the projectile when it reached the target? How do the real values ​​of the sought quantities differ from the calculated ones
SOLUTION

A body is thrown vertically upward with a speed of 30 m/s. At what height and after what time the speed of the body (modulo) will be 3 times less than at the beginning of the ascent
SOLUTION

The BALL was thrown vertically upwards twice. The second time he was told the speed, 3 times greater than the first time. How many times higher does the ball rise on the second throw?
SOLUTION

A body is thrown vertically upward with a speed of 20 m/s. Write the equation of motion y = y(t). Find the time interval after which the body will be at a height of: a) 15 m; b) 20 m; c) 25 m. Indication. The Y axis is directed vertically upwards; accept that at t = 0 y = 0
SOLUTION

A ball is thrown vertically upwards from a balcony 25 m above the ground with a speed of 20 m/s. Write a formula for the dependence of the coordinate on time y(t), choosing as the origin: a) the point of throw; b) the surface of the earth. Find the time it takes for the ball to hit the ground.

It remains for us to consider the case when the load, together with the scales, makes a free fall, that is, when the scales are simply let go of the hands (Fig. 129). Experience shows that during free fall, the pointer of the scales is set on the pool: the weight is equal to zero. And this is understandable. After all, when the load falls under the influence of attraction to the Earth, the spring of the scales “itself follows it” (see Fig. 129). Therefore, it does not deform. But if the spring does not deform, then no force from its side acts on the load attached to it. The load is therefore also not deformed and also does not act on the spring. The load became weightless.

The fact that in free fall the weight of a body is zero follows directly from the formula

When a body is in free fall, therefore,

Under this condition, the dispute does not interact with the body.

The reason for weightlessness is that the force of universal gravitation imparts the same accelerations to the body and its support. Therefore, any body that moves only under the influence of the forces of universal gravitation is in a state of weightlessness.

It is in such conditions that a freely falling body is located.

This amazing fact is illustrated by the following interesting experience (Fig. 130). A block is fixed on the tripod, through which the thread is thrown. At the end of this thread, a cup with two weights of a sufficiently large mass is suspended. The top weight fits snugly against the bottom weight. The other end of the thread is attached to a tripod. A strip of thin paper is placed between the weights. Its free end is held motionless in the hand. If the load is lowered slowly, then the paper, stretching, will break, because the static friction force acts on the clamped end of the strip. Now let's replace the strip of paper with a new one and repeat the experiment in such a way that the weight falls freely. When the load falls, the strip of paper remains untorn in the hands. This means that when falling, the loads did not press on each other and the static friction force was equal to zero. This proves that weights in free fall are in a state of weightlessness.

Exercise 31

1. Is a body thrown vertically upwards in a state of weightlessness? Ignore friction in the air.

2. To the frame, which can slide along two guide rods (Fig. 131), various loads are suspended on two identical springs. If you burn the thread with which the frame is strengthened, the frame will fall freely (friction is small and can be neglected) and in this case, the deformation of the springs will disappear. Explain why the deformations of the springs disappear during free fall of the frame.

Introductory control in physics 8kl

OPTION #2

Complete the sentence with one word:

1. The physical quantity that characterizes the inertia of a body is called ____________________

2. The force with which the Earth attracts bodies to itself is called

____________________

3. The force that prevents movement is called_______________________________________

4. Device for measuring length ____________________

5. A wheel with a groove, reinforced in the cage is ___________

6. Device for measuring pressure _________________

TEST

1. The smallest particles that make up substances are called: a) molecules, b) microparticles, c) grains.

2. Diffusion can be slowed down if: a) cool the body, b) heat it, c) move it from one table to another.

3. What general properties are characteristic of solids: a) they have their own shape and volume, b) they are easily compressed, c) they are practically not compressible.

4. What formula can be used to calculate body volume?a) F= mg. b) p= m: v. d) V= S: te) V= abc

5. What force makes all bodies fall to the Earth? a) the force of friction, b) the force of elasticity, c) the force of gravity, d) the weight of the body.

6. What formula can be used to calculate gravity?a) F= mgb) F= mgh. d) p= F: Se) V= S: t

7. What is the unit of pressure? a) Pa b) N c)m/s d)kg

8. Which of the astronauts was the first to fly into space? a) Gagarin b) Titov c) Tereshkova d) Leonov.

9. By what formula can work be calculated?a) F= pghb) A= FSd) N= A: t

10. the body performs mechanical work when a) it moves, b) a force acts on it, c) a force acts on it and it

PHYSICS TESTS 8th grade

TEST 1 Thermal motion. Temperature.

1. Diffusion occurs faster if a) the movement of molecules slows down b) the movement of molecules stops c) the speed of movement of molecules increases

2. What is the difference between warm water and cold water?

a) the speed of movement of molecules

b) the structure of molecules

c) transparency

3. Which of the phenomena refers to thermal?

a) the rotation of the earth around the sun

b) rainbow

c) melting snow

4. What is the trajectory of gas molecules?

a) in a straight line

b) along a curvilinear

c) along a broken line

5. In what bodies can molecules vibrate, rotate, move relative to each other?

a) in gases

b) in liquids

c) in solids

6. Body temperature related

a) with the kinetic energy of the body

b) with the potential energy of the body

c) with average kinetic energy of molecules

TEST #2 Internal energy

1. The kinetic energy of a body depends a) only on the mass of the body b) only on the speed of the body c) on the mass and on the speed of the body

2. When a body is released from the hands, a) there is a transition of potential energy into kinetic energy b) there is a transition of kinetic energy into potential energy c) .kinetic and potential energies do not change

3. The mechanical energy of a piece of plasticine that has fallen to the floor, a) will not change b) will disappear without a trace c) will turn into another form of energy

4. What energy is called the internal energy of the body? a) body motion energy b) interaction energy of body parts c) kinetic and potential energies of body parts

5. The internal energy of a body depends a) on the speed of the body b) on the temperature of the body and its state (solid, liquid, gaseous) c) on the position of the body relative to other bodies

6. Can a body not have internal energy? a) it can, if the body has a very low temperature b) it can, if the body has no mechanical energy c) it cannot under any circumstances

Literature: SYPCHENKO G.V.

PHYSICS tests 8th class Saratov: Lyceum, 2012.-80s

Internet resource

1. You are well aware that bodies fall to the ground if they are not held by a support, a suspension thread, a hand, etc. When a body falls, its speed increases, i.e., the fall of bodies is an accelerated movement.

If we simultaneously release metal and paper circles of the same size from our hands from a certain height and observe their movement, then we will notice that the metal circle will fall to the ground before the paper one. It can be assumed that the time of falling bodies depends on their mass. To verify this, let's take two identical sheets of paper, crumple one of them and simultaneously release them from our hands. The crumpled piece of paper will fall to the ground first. Therefore, different fall times are not related to the mass of the bodies.

Obviously, a crumpled sheet of paper and a smooth one experience different air resistance when falling. This assumption can be confirmed experimentally.

Take a thick-walled tube, one end of which is sealed, and the other is equipped with a tap. A pellet, a piece of cork, and a bird's feather are placed in the tube (Fig. 33). If you quickly turn the tube over, then these bodies will fall to its bottom. You can see that the pellet will fall before everyone else, and the feather - after all the bodies. If now the air is pumped out of the tube and, having closed the tap, it is turned over again, then all three bodies will reach the bottom of the tube at the same time, despite the fact that they have different shapes and masses. Therefore, all bodies in airless space (in vacuum) fall with the same acceleration, which is called free fall acceleration.

The fall of bodies in airless space is called free fall.

2. The free fall of bodies is a uniformly accelerated motion.

The free fall acceleration is always directed towards the center of the Earth and has the same value for all bodies at their same initial position relative to the Earth's surface.

Indeed, as you already know, the modulus of displacement of a body during uniformly accelerated motion without an initial velocity is calculated by the formula: s= . From the experiment described above, it follows that a pellet, a piece of cork, and a bird's feather make the same movements in the same intervals of time, so they all move with the same acceleration.

A body thrown vertically upwards also moves uniformly with the acceleration of free fall. In this case, the velocity and acceleration vectors of the body are directed in opposite directions, and the velocity modulus decreases with time.

3. Free fall acceleration is denoted by the letter g. As you know from the 7th grade physics course, the acceleration of free fall depends on the geographical latitude of the area. At the latitude of Moscow near the Earth's surface, it is equal to 9.81 m/s 2 . When solving problems, if high accuracy of the result is not required, take g\u003d 10 m / s 2.

The free fall acceleration depends on the height of the body above the Earth's surface. The higher the body is raised, the weaker it is attracted to the Earth and the lower the acceleration of free fall. For example, for passenger aircraft with a maximum altitude of about 10 km above sea level, the acceleration due to gravity at this altitude is 9.78 m/s 2 . For the heights at which modern fighters fly, a more significant decrease in the acceleration of free fall is characteristic. So, at an altitude of 18 km, it is equal to 9.72 m / s 2.

The acceleration of gravity is even less important at altitudes where the orbits of artificial Earth satellites and space stations are located. Thus, the maximum height of the first artificial Earth satellite relative to sea level was 947 km. The free fall acceleration at this height is 7.41 m/s 2 .

4 * . Free fall was studied by an Italian scientist, one of the founders of classical mechanics, Galileo Galilei (1564-1642) at the end of the 16th century. He dropped from the Leaning Tower of Pisa at the same time a ball weighing about 200 g and a body weighing 40 kg, which has a cigar shape. Contrary to the opinion that existed at that time, the bodies reached the surface of the Earth almost simultaneously. The ball was only a few centimeters behind. Galileo did not have accurate instruments for measuring time, he used an hourglass, so the value of the acceleration of free fall was measured by him with a large error. In particular, in his work “Dialogue on the two main systems of the world - Ptolemaic and Copernican”, Galileo argued that bodies fell from a height of 60 m for 5 s and, based on these data, obtained the value of the free fall acceleration almost 2 times less than that obtained in present time.

To improve the accuracy of the experiment on the study of uniformly accelerated motion and free fall, in particular, Galileo studied the sliding of balls from an inclined plane. He experimentally established the proportionality of the path traversed by the ball to the square of time and the law of the ratio of the paths traversed by it in successive equal intervals of time.

5. Problem solution example

Two bodies simultaneously begin to move: one vertically upwards with a speed of 20 m/s, the other vertically downwards from a height of 60 m without initial velocity. Determine the time and coordinate of the meeting point of the bodies.

We write the equation of motion in projections onto the axis OY:

y = y 0 + v 0y t + .

For the first body, this equation has the form:

y 1 = y 01 + v 01y t + .

Given that y 01 = 0; v 01y = v 01 ; g y = –g, we get

y 1 = v 01 t – .

Equation of motion of the second body:

y 2 = y 02 + v 02y t + .

Because the y 02 = h; v 02y = 0; g y = –g, then

y 2 = h – .

At the moment of the meeting of the bodies, their coordinates will be the same: y 1 = y 2 = y. Then v 01 t –= h – ; v 01 t = h.

Hence the time of the meeting of the bodies t = ;

t== 3 s.

We find the coordinate of the meeting place of the bodies from the equation of motion of the first body.

y= 20 m/s 3 s –= 15 m.

Answer: t= 3 s; y= 15 m.

Questions for self-examination

1. What movement is called free fall?

2. What type of mechanical motion is free fall?

3. How to experimentally prove that the acceleration of free fall is the same for all bodies at a given point in space?

4. What does free fall acceleration depend on?

Task 8

1. A ball falls to the ground from a height of 20 m with an initial velocity of zero. How long will it take to reach the earth's surface? What is the speed of the ball when it hits the ground? At what height relative to the ground will the ball be in 1 second after the start of the fall? What speed will it have at this point in time? Ignore air resistance.

2. According to task 1, plot the dependency graphs of the velocity projection on the axis Y and the modulus of the ball's speed versus time, if the axis Y directed: a) vertically down; b) vertically up.

3. At what height relative to the Earth's surface will two balls meet if one is thrown vertically upward with a speed of 10 m/s, and the other falls from a height of 10 m without initial velocity? The balls start moving at the same time. What speed relative to the ground will the balls have at this height? Ignore air resistance. Build graphs of the dependence of the coordinates of each ball on time and determine from the graph the time and coordinate of the place of their meeting * .

4 * . Calculate the free fall acceleration using the data obtained by Galileo.

5. Build graphs of the dependence of the projection of the speed of bodies on time according to the problem considered in § 8 * . Based on this data, plot the dependence of the coordinates of each body on time and graphically determine the time and coordinate of the meeting point of the bodies.