7.1: A wooden block measuring 40 cm ｘ 10 cm ｘ 5 cm has a mass 850 g. Find the density of wood. Ans. (425 kgm⁻³

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7.2: What would be the volume of ice formed by freezing 1 litre of water?  Ans. (1.09 litre)


7.3: Calculate the volume of the following objects:
(i) An iron sphere of mass 5 kg, the density of iron is 8200 kgm⁻³. Ans. (6.1x10⁻⁴m³)
(ii) 200 g of lead shot having density 11300 kgm⁻³. Ans.(1.77x10⁻⁵m³)
(iii) A gold bar of mass 0.2 kg. The density of gold is 19300 kgm⁻³ Ans. (1.04x10⁻⁵m³)


7.4: The density of air is 1.3 kgm⁻³. Find the mass of air in a room measuring 8m x 5m x 4m. Ans. (208 kg)


7.5: A student presses her palm by her thumb with a force of 75 N. What would be the pressure under her thumb having contact area 1.5 cm²? Ans. (5ｘ10⁵ Nm⁻²)



7.6: The head of a pin is a square of side 10 mm. Find the pressure on it due to a force of 20 N. Ans. (2x10⁵ Nm⁻²)


7.7: A uniform rectangular block of wood 20 cm x 7.5 cm x 7.5 cm and of mass 1000g stands on a horizontal surface with its longest edge vertical. Find (i) the pressure exerted by the block on the surface (ii) density of the wood. Ans. (1778 Nm⁻², 889 kgm⁻³)


7.8: A cube of glass of 5 cm side and mass 306 g, has a cavity inside it. If the density of glass is 2.55 gcm⁻³ . Find the volume of the cavity. Ans. (5 cm³)

7.9: An object has weight 18 N in air. Its weight is found to be 11.4 N when immersed in water. Calculate its density. Can you guess the material of the object? Ans. (2727 kgm⁻³, Aluminum)


7.10: A solid block of wood of density 0.6 gcm⁻³ weighs 3.06 N in air. Determine (a) volume of the block (b) the volume of the block immersed when placed freely in a liquid of density 0.9 gcm⁻³? Ans. (510 cm³, 340 cm³)



7.11: The diameter of the piston of a hydraulic press is 30 cm. How much force is required to lift a car weighing 20 000 N on its piston if the diameter of the piston of the pump is 3 cm? Ans. (200 N)


7.12: A steel wire of cross-sectional area 2x10⁻⁵ m² is stretched through 2 mm by a force of 4000 N. Find the Young's modulus of the wire. The length of the wire is 2 m. Ans. (2 ｘ 10¹¹ Nm⁻²)