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

Answer- Examples of push and pull situation to change the state of motion of an object-

Push-

• We push a box to move from place to another place.
• We push the door to close it.

Pull–

• We pull drawer/gate to open.
• We pull the rope to draw water from the well.

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

Answer- Following are the examples of situations in which applied force causes a change in the shape of an object-

• Squeezing of plastics bottles.
• Making a chapati from a ball of dough.
• Pressing clay between the fingers to make different structures.

3. Fill in the blanks in the following statements.

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

Answer– pull

(b) A charged body _______an uncharged body towards it.

Answer– attracts

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

Answer– push

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

Answer– repel

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 _____________.

Answer– shape

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

Answer– muscular

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

Answer– contact

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

Answer– gravity, friction

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.

Answer– We use the muscular force in squeezing the piece of the lemon to extract its juice. The muscular force is exerted on lemon between our fingers. As a result, the shape of the lemon changed.

(b) Taking out paste from a toothpaste tube.

Answer– We use the muscular force to take out the paste from a toothpaste tube. Muscular force is exerted on the toothpaste tube between our fingers. As a result, the shape of the toothpaste tube changed.

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

Answer– The load exerts a force on the spring and pushes the spring downward. As a result, the spring gets stretched and its shape gets changed.

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

Answer– The athlete pushes the ground with his feet and exerts a muscular force on the ground which allows him to jump over the bar at a certain height. As a result, his state of motion gets changed.

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?

Answer– A blacksmith hammers (applies a muscular force) on a hot piece of iron while making a tool. The force due to hammering changes the shape of the piece of iron so that it can be moulded in the desired shape.

Q7. 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?

Answer– The ballon becomes electrically charged due to rubbing with a piece of synthetic cloth. As we know a charged body attracts an uncharged body. Hence, the inflated balloon was found stuck to the wall when pressed after rubbing with a piece of synthetic cloth. Therefore, the electrostatic force is responsible for the attraction between the balloon and the wall.

Q8. Name the force 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.

Answer-Here two forces are acting on the bucket-

• Muscular Force (upward)
• Gravitational Force (downward)

Both forces are equal in magnitude but opposite in direction. Hence, the net force acting on the bucket is zero. Thus, they cancel each other effects. As a result, they don’t bring a change in the state of motion of the bucket.

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.

Answer– When a rocket is fired upward to launch a satellite in its orbit, there are many forces acting on the rocket immediately after leaving the launching pad such as gravitational force, the frictional force due to atmosphere, lift, drag, thrust etc.

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.

Answer– (d) atmospheric pressure.

Explanation: When the bulb of a dropper is pressed, the pressure inside the dropper decreases and this causes the water to go inside the dropper to maintain the equilibrium.