Solution:

Examples of Situations where Push or Pull Changes the State of Motion of Objects

Push:

• When you push a stationary book on a table to make it move.
• When a football player pushes the ball with their foot to make it roll across the field.

Pull:

• When you pull a sled to move it across the snow.
• When you pull a drawer to open it.

Solution:

Examples of Situations Where Applied Force Causes a Change in Shape of an Object

1. When a person presses a rubber ball, the shape of the ball changes due to the applied force. The ball becomes compressed and may change its shape temporarily.

2. When a metal rod is bent by applying force at its ends, the shape of the rod changes. This change in shape is due to the deformation caused by the applied force.

Solution:

(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 $push$ it.

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

Solution:

(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.

Solution:

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

Agent exerting the force: Fingers

Object on which force acts: Lemon

Effect of the force: The force deforms the lemon, causing the juice to be extracted.

(b) Taking out paste from a toothpaste tube.

Agent exerting the force: Hands (fingers)

Object on which force acts: Toothpaste tube

Effect of the force: The force deforms the toothpaste tube, causing the paste to be pushed out.

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

Agent exerting the force: Gravity

Object on which force acts: Load (mass)

Effect of the force: The force stretches the spring, causing it to elongate.

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

Agent exerting the force: Athlete's muscles

Object on which force acts: Athlete's body

Effect of the force: The force propels the athlete's body upward to clear the bar.

Solution:

Effect of Force Due to Hammering on a Hot Piece of Iron

When a blacksmith hammers a hot piece of iron, the force due to hammering has several effects on the iron:

• The force applied by the hammer increases the shape of the iron by causing deformation. Since the iron is hot, it is more malleable and easier to change its shape under force.
• The hammering also causes the particles in the iron to move and rearrange, making the iron more compact and changing its structure.
• As the iron is repeatedly hammered, its temperature may also change, and the process of hammering can lead to the formation of new crystalline structures in the iron, depending on how hot it is and how much force is applied.

The force applied helps in shaping and refining the iron for the intended tool.

Solution:

Force Responsible for the Attraction Between the Balloon and the Wall

When an inflated balloon is rubbed with a synthetic cloth, it gains a static electric charge. This is due to the transfer of electrons between the balloon and the cloth, causing the balloon to become negatively charged. When the balloon is pressed against a wall, the charges on the balloon induce a charge on the surface of the wall. The wall may become positively charged near the surface in response to the balloon's negative charge. The attraction between the opposite charges on the balloon and the wall is the force responsible for the balloon sticking to the wall. This force is called electrostatic force.

Solution:

Forces Acting on a Plastic Bucket Containing Water Held Above Ground Level

The forces acting on the plastic bucket containing water held above ground level are:

• Gravitational Force (Weight): The weight of the bucket and water acts downward towards the Earth.
• Upward Force (Applied Force): The hand applies an upward force to hold the bucket against gravity.
• Air Resistance: There is a small air resistance acting on the bucket, opposing its motion through the air, though this is negligible in this case.

Discussion on the Forces and State of Motion

The forces acting on the bucket are balanced. The upward force exerted by the hand exactly cancels out the downward gravitational force acting on the bucket. Since the net force on the bucket is zero, there is no change in its state of motion. The bucket remains stationary and does not accelerate, according to Newton's First Law of Motion, which states that an object at rest will remain at rest unless acted upon by an unbalanced force.

Solution:

Forces Acting on the Rocket Immediately After Leaving the Launching Pad

The two forces acting on the rocket are:

• Gravitational Force (Weight): The force due to gravity pulling the rocket downward.
• Thrust: The force exerted by the rocket engines pushing it upward.

Solution:

4. 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. CORRECT