Q20 of 31 Page 143

Why does a block f plastic released under water come up to the surface of water?

The density of plastic is less than that of water, so the force of buoyancy on plastic block will be greater than the weight of plastic block displaced. Hence, the acceleration of plastic block will be in upward direction, and comes up to the surface of water.


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17

A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet.

 18

A ball thrown up vertically returns to the thrower after 6 s, find:

(a) The velocity with which it was thrown up,


(b) The maximum height it reaches, and


(c) Its position after 4 s.

 19

In what direction does the buoyant force on an object immersed in a liquid act?

 21

The volume of 50 g of a substance is 20 cm3. If the density of water is 1 g cm-3, will the substance float or sink?