1. Give two examples each of situations in which you push or pull to change the state of motion of objects.
Ans:
1. Pull Situations:
a) To open a drawer, we pull it, changing its state of motion.
b) While drawing water from a well, the rope is pulled, changing the state of motion of the bucket.
2. Push Situations:
a) A football is pushed by a player’s foot, changing its state of motion.
b) To move a heavy box from one room to another, we push it, changing its motion.
2. Give two examples of situations in which applied force causes a change in the shape of an object.
Ans:
The forces that change the shape of an object are:
i) Pressing clay between the hands causes it to deform and take a new shape.
ii) Squeezing a plastic bottle changes its shape.
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 another magnet.
Ans:
(a).pull at the rope.
(b).attracts
(c) pull or push
(d) repels
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 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
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 that due to friction of 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:
(a) Squeezing a piece of lemon between the fingers to extract its juice:
Agent: Fingers
Object: Lemon
Effect: Changes the shape of the lemon, causing juice to come out.
(b) Taking out paste from a toothpaste tube:
Agent: Fingers
Object: Toothpaste tube
Effect: Changes the shape of the tube, forcing the paste out.
(c) A load suspended from a spring while its other end is fixed to a wall:
Agent: Load
Object: Spring
Effect: Stretches the spring, changing its shape.
(d) An athlete making a high jump to clear the bar at a certain height:
Agent: Athlete’s feet
Object: Ground
Effect: Changes the athlete’s state of motion, allowing them to jump over the bar.
6. A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Ans:
When a blacksmith hammers a hot piece of iron, the force due to hammering changes the shape of the iron. The iron becomes malleable when heated, and the muscular force applied through hammering helps mold it into the desired shape.
7. 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 stuck to the wall. What force might be responsible for the attraction between the balloon and the wall?
Ans:
When a balloon is rubbed with a synthetic cloth, it becomes charged due to static electricity. A charged balloon creates an electrostatic force that attracts the wall, which is uncharged. This electrostatic force is responsible for the balloon sticking to the wall.
Solution:
The forces acting on the bucket are:
Muscular force applied by the hand to hold the bucket.
Force of gravity pulling the bucket towards the ground.
These two forces are equal in magnitude but opposite in direction, leading to a net force of zero. Since the net force is zero, there is no change in the state of motion of the bucket, and it remains stationary.
8. 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.
Ans:
The forces acting on the bucket are:
Muscular force applied by the hand to hold the bucket.
Force of gravity pulling the bucket towards the ground.
These two forces are equal in magnitude but opposite in direction, leading to a net force of zero. Since the net force is zero, there is no change in the state of motion of the bucket, and it remains stationary.
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 are:
Gravitational force: Pulling the rocket downward toward the Earth.
Frictional force: Caused by air resistance opposing the upward motion of the rocket.
10. 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) gravity of the earth
(c) shape of rubber bulb
(d) atmospheric pressure
Ans:
(d) Atmospheric pressure
When the bulb is pressed, the air inside the dropper escapes as bubbles. On releasing the bulb, the atmospheric pressure acting on the surface of the water forces the water to rise into the dropper.