Q15 of 16 Page 343

Define relative density of a solid. State its unit. How is it related to its density? Write mathematical expression for relative density. What conclusion do you draw if relative density of a substance is (a) greater than 1, (b) less than 1 and (c) equal to 1?

Relative density refers to the ratio of the density of a substance to the density of water.

Relative Density =


(a) greater than 1: If the relative density is greater than 1, that means that the density of a substance is greater than the density of water.


(b) less than 1: If the relative density is less than 1, that means that the density of a substance is less than the density of water.


(c) equal to 1: If the relative density is equal to 1, that means that the density of a substance is equal to the density of water.


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(a) What happens to the ball?


(b) Give a reason for this phenomenon.

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A wooden block is kept on a table top. The mass of the wooden block is 5 kg and its dimensions are 40 cm × 20 cm × 10 cm. Find the pressure exerted by the wooden block on the table top if it is made to lie on the table top with its sides of dimensions (a) 20 cm × 10 cm and (b) 40 cm × 20 cm.

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State Archimedes’ principle. List its two applications.

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It was raining heavily one day. Prateek made a paper boat and started playing with it in a water pool at road side. He then got his toys and dolls and made them boat riders the boat sank in water. Prateek did not lose courage. He made another boat and used lighter toys as passengers and this time boat did not sink in water.

(a) Why did not sink when loaded with dolls and toys?


(b) Which force is exerted by water on objects immersed in it?


(c) What qualities are shown by Prateek?