Force(NCERT Solutions)

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

Ans-

Examples of push to change the state of motion of objects

(a) Pushing the box to move it from one place to other.

(b) Pushing the knife to cut vegetables.

Examples of pull to change the state of motion of objects

(a) Pulling the door of room to open it.

(b )Pulling the bag from the chair.

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

Ans-

(a)A rubber band elongated when stretched (Force).

(b) Pressing (Force) paper to make a ball.

(3)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 the another magnet.

Ans-

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

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

(c) To move a loaded trolley we have to push or pull it.

(d) The north pole of a magnet repel the north pole of the another magnet.

(4) 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 gapes 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 __________.

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

(d) While the arrow moves towards its target, the forces acting on it are due to ________and ________ of the air.

Ans-

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

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

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

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

(5)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.

Ans-

schoolhelpbygunjan.wordpress.com|Solution of Question No 5 |NCERT Forc CLass 7

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

Ans-

Force can change the shape of objects. When a blacksmith hammers a hot piece of metal, he exerts force on the metal with hammer. Therefore, by doing hammering continuously he can able to make tool from it.

(7) An inflated balloon 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?

Ans-

Electrostatic force is responsible for the attraction between the balloon and the wall. When an inflated balloon rubbed with a piece of synthetic cloth, it gets charged due to electrostatic force exerted by the synthetic cloth. Therefore, balloons sticks on the wall.

(8)Name the forces acting on a plastic bucket contacting 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.

Ans-

Muscular force is acting on a plastic bucket contacting water held above ground level in our hand. The forces acting on the bucket do not bring a change in its state of motion because forces are balanced forces. The muscular force exerted by our hand is equal and opposite in direction to the gravity force exerted on the bucket by the earth.

(9) 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.

Ans-

The two forces acting on the rocket immediately after leaving the launching pad are

(a)Friction force exerted by the air.

(b) Gravitational force exerted by the earth.

(10) 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.

Ans- pressure of water.

 

Helping Topics

Force and laws of motion

Practice sheet class 8

Picture1

 

 

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