NCERT Class VIII Science Solutions: Chapter 11-Force and Pressure Part 3

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Question 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.

Answer:

The force acting on a plastic bucket are:

  • Gravitational force: It is acting downwards.

Image result for gravitational force

Gravitational Force

  • Muscular force: It is applied by our hands to lift the bucket in upward direction.

The force resulting due to the action of muscles is called muscular force.

This image shows muscular force

Muscular Force

Although these forces are acting on the bucket but no change is found in its state of motion because the two forces are balancing each other and as a result net force is zero.

Question 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.

Answer:

Two forces acting on the rocket immediately after leaving the launching pad are:

  • Frictional force due to air.

  • Force of gravity pulling in downward direction.

Question 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

  1. pressure of water

  2. gravity of the earth

  3. shape of rubber bulb

  4. atmospheric pressure

Answer:

The rise of water in the dropper is due to (D) atmospheric pressure.