67. When a weight of 10 kg is suspended from a copper wire of length 3 metres and diameter 0.4 mm, its length increases by 2.4 cm. If the diameter of the wire is doubled, then the extension in its length will be
(a) 9.6 cm (b) 4.8 cm
(c) 1.2 cm (d) 0.6 cm
Answer-d
(18)