21.A 100 N force stretches the length of a hanging wire by 0.5 mm. The force required to stretch a wire, of the same material and length but having four times the diameter, by 0.5 mm is

22.For a given material, the Young s modulus is 2.4 times that of modulus of rigidity. Its Poisson s ratio is

23.Two wires of the same material and same are stretched by the same force. Their lengths are in the ratio 2 : 3. Their elongations are in the ratio

24.When a weight of 5 kg is suspended from a copper wire of length 30 m and diameter. 0.5, the length of the wire increases by 2.4 cm. If the diameter is doubled, the extension produced is

25.When a 4 kg mass is hung vertically on a light spring that obeys Hooke s law, the spring stretches by 2 cm. The work required to be done by an external agent in stretching this spring by 5 cm will be