94. A 5 m long aluminium wire

A 5 m long aluminium wire ( Y=7×10¹⁰ N/m²) of  diameter 3 mm supports a 40 kg mass. In order to have the same elongation in a copper wire ( Y=12×10¹⁰ N/m²) of the same length under the same weight, the diameter should now be, in mm

(a)   1.75                                         (b)   1.5

(c)    2.5                                          (d)   5.0

Answer-c