Ncert solutions science class 8 Solutions for Chapter 11 force and pressure

To draw water from a well we have to __________ at the rope.

To move a loaded trolley we have to __________ it.

The north pole of a magnet __________the north pole of another magnet.

A charged body __________ an uncharged body towards it.

Give two examples each of situations in which you push or pull to change the state of motion of objects

Give two examples each of situations in which you push or pull to change the state of motion of objects.

Q1) Give two examples each of situations in which you push or pull to change the state of motion of objects.

In Fig , two boys A and B are shown applying force on a block. If the block moves towards the right,

which one of the following statements is correct?

(a) Magnitude of force applied by A is greater than that of B.

(b) Magnitude of force applied by A is smaller than that of B.

(c) Net force on the block is towards A.

(d) Magnitude of force applied by A is equal to that of B.

Q2) Give two examples of situations in which applied force causes a change in the shape of an object.

Give two examples of situations in which applied force causes a change in the shape of an object.

In the circuit shown in Fig., when the circuit is completed, the hammer strikes the gong. Which of

the following force is responsible for the movement of a hammer?

(a) gravitational force alone

(b) electrostatic force alone

(c) magnetic force alone

(d) frictional force alone

Give two examples of situations in which applied force causes a change in the shape of an object.

During dry weather, while combing hair, sometimes we experience hair flying apart. The force responsible for this is

(a) force of gravity.

(b) electrostatic force.

(c) a force of friction.

(d) magnetic force.

Q3) Fill in the blanks in the following statements.

(a) To draw water from a well we have to __________ at the rope.

(b) A charged body __________ an uncharged body towards it.

(c) To move a loaded trolley we have to __________ it.

(d) The north pole of a magnet __________the north pole of another magnet.

Fill in the blanks in the following statements.

(a) To draw water from a well we have to __________ at the rope.

(b) A charged body __________ an uncharged body towards it.

(c) To move a loaded trolley we have to __________ it.

(d) The north pole of a magnet __________the north pole of another magnet.

Fig. shows a container filled with water. Which of the following statements is correct about pressure of water?

(a) Pressure at A> Pressure at B> Pressure at C

(b) Pressure at A=Pressure at B=Pressure at C

(c) Pressure at A< Pressure at B>Pressure at C

(d) Pressure at A< Pressure at B

An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins t move towards the target. Based on this information fill up the gaps in the following statements using th following terms. muscular, contact, non-contact, gravity, friction, shape, attraction

(a) To stretch the bow, the archer applies a force that causes a change in its __________.

(b) The force applied by the archer to stretch the bow is an example of __________ force.

(c) The type of force responsible for a change in the state of motion of the arrow is an example of a__ force.

(d) While the arrow moves towards its target, the forces acting on it are due to __________ and that due to __________ of air

Q4) An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms.

muscular, contact, non-contact, gravity, friction, shape, attraction

(a) To stretch the bow, the archer applies a force that causes a change

in its __________.

(b) The force applied by the archer to stretch the bow is an example of

__ force.

(c) The type of force responsible for a change in the state of motion of the

arrow is an example of a __________ force.

(d) While the arrow moves towards its target, the forces acting on it are

due to __________ and that due to __________ of air.

An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms.

muscular, contact, non-contact, gravity, friction, shape, attraction

(a) To stretch the bow, the archer applies a force that causes a change in its __________.

(b) The force applied by the archer to stretch the bow is an example of __________ force.

(c) The type of force responsible for a change in the state of motion of the arrow is an example of a __________ force.

(d) While the arrow moves towards its target, the forces acting on it are due to __________ and that due to __________ of air

In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

(a) Squeezing a piece of lemon between the fingers to extract its juice.

Q5) In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

(a) Squeezing a piece of lemon between the fingers to extract its juice.

(b) Taking out paste from a toothpaste tube.

(c) A load suspended from a spring while its other end is on a hook fixedto a wall.

(d) An athlete making a high jump to clear the bar at a certain height.

Two objects repel each other. This repulsion could be due to

(a) frictional force only

(b) electrostatic force only

(c) magnetic force only

(d) either a magnetic or an electrostatic force

In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

Taking out paste from a toothpaste tube.

In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

(a) Squeezing a piece of lemon between the fingers to extract its juice.

(b) Taking out paste from a toothpaste tube.

(c) A load suspended from a spring while its other end is on a hook fixed to a wall.

(d) An athlete making a high jump to clear the bar at a certain height

In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

A load suspended from a spring while its other end is on a hook fixed to a wall.

In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

An athlete making a high jump to clear the bar at a certain height

A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

Q6) A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

Which one of the following forces is a contact force?

(a) force of gravity

(b) force of friction

(c) magnetic force

(d) electrostatic force

A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

Q7) An inflated balloon was pressed against a wall after it had been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

A water tank has four taps fixed at points A, B, C, D as shown in Fig. The water will flow out at the same pressure from taps at

(a) B and C

(b) A and B

(c) C and D

(d) A and C

A brick is kept in three different ways on a table as shown in Fig. . The pressure exerted by the brick

on the table will be

(a) maximum in position A C

(b) maximum in position B

(c) maximum in position

(d) equal in all cases.

Q8) Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion?

Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.

Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.

A ball of dough is rolled into a flat chapatti. Name the force exerted to change the shape of the dough.

A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.

Q9) A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching

pad.

A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.

Where do we apply a force while walking?

When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to

(a) pressure of water.

(b) gravity of the earth.

(c) shape of rubber bulb.

(d) atmospheric pressure

When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to

(a) pressure of water.

(b) gravity of the earth.

(c) shape of rubber bulb.

(d) atmospheric pressure

Q10) When we press the bulb of a dropper with its nozzle kept in water,The air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to

(a) pressure of water

(b) the gravity of the earth

(c) the shape of a rubber bulb

(d) atmospheric pressure

A girl is pushing a box towards east direction. In which direction should her friend push the box so that it moves faster in the same direction?

During dry weather, clothes made of synthetic fiber often stick to the skin. Which type of force is responsible for this phenomenon?

During dry weather, clothes made of synthetic fiber often stick to the skin. Which type of force is responsible for this phenomenon?

While sieving grains, small pieces fall down. Which force pulls them down?

Does force of gravity act on dust particles?

A gas filled balloon moves up. Is the upward force acting on it larger or smaller than the force of gravity?

Does the force of gravitation exist between two astronauts in space?

A chapati maker is a machine that converts balls of dough into chapatis. What effect of force comes into play in this process?

Fig. shows a man with a parachute. Name the force which is responsible for his downward motion.

Will he come down with the same speed without the parachute?

Two persons are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction. What do you infer about the magnitudes and direction of the forces applied?

Two thermocol balls held close to each other move away from each other. When they are released, name the force which might be responsible for this phenomenon. Explain.

Fruits detached from a tree fall down due to force of gravity. We know that a force arises due to the interaction between two objects. Name the objects interacting in this case.

A man is pushing a cart down a slope. Suddenly the cart starts moving faster and he wants to slow it down. What should he do?

Fig. shows a car sticking to an electromagnet. Name the forces acting on the car? Which one of them is larger?

An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow ultimately falls down.

It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.

Two rods of the same weight and equal length have different thicknesses. They are held vertically on the surface of sand as shown in Fig. . Which one of them will sink move? Why?

Two women are of the same weight. One wears sandals with pointed heels while the other wears sandals with flat soles. Which one would feel more comfortable while walking on a sandy beach? Give reasons for your answer.

It is much easier to burst an inflated balloon with a needle than by a finger. Explain.

Observe the vessels A, B, C and D shown in Fig. carefully.

Volume of water taken in each vessel is as shown. Arrange them in the order of decreasing pressure at the base of each vessel. Explain.