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3. V x h x d.

4. V x p x g.
8. A ball floats on the surface of water in a container exposed to the atmosphere. If
the container is now covered and the air is pumped out, then

1. the ball will remain at its former depth.
2. the ball will rise somewhat.

3. the ball will sink to the bottom.

4. the ball will sink a bit.
9. A lactometer is based on

1. Universal law of Gravitation.

2. Archimedes' principle.
3. Centripetal force.

4. Newton's second law of motion.

10. Nitu immerses a solid into a liquid. She finds that the weight of a body is exactly
equal to the weight of the liquid displaced by it. The body will

1. sink in the liquid.

2. float on the surface of the liquid.
3. go to the bottom and come back to the surface again.

4. remain suspended in middle of the liquid.

Conceptual questions

1. Why does a body lose weight when immersed in a liquid? (Average)
2. why is it easier for a person to swim in sea water than in fresh water?(Board)
3. Why is it easier to lift a mighty stone under water but difficult to lift it in air?
(BOARD)
4. In what direction does the buoyant force on an object immersed in a liquid act?
(Average)

NUMERICALS:
1. A block of wood with length = 2.5 m, width = 0.5 m and height = 0.4
m. The density of water is 1000 kg/m3. If the block is placed in the water, what is
2
the buoyant force… Acceleration due to gravity is 10 m/s .
2. An object of 40 N weight when immersed in water loses 10 N weight. Will the
object float or sink? Why?
3. A sphere of mass 5 kg and volume 2.2 × 10–4 m3 is completely immersed in
water. Find the buoyant force exerted by water on the sphere. Density of water =
2
1000 kg/m3 (Given: g = 9.8m/s ).

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