Question

Two wires are made of the same material and have the same volume.The first wire has cross sectionel area a and the secomd wire has cross sectional area 3a.If the length of the first wire is increased by ∆ on applyimg a force f,hkw much force is needed to stretch the secomd wire by the same amount

Answer 1

Since the two wires have same volume.

Length of wire 1 =l

Length of wire 2 =l3

Area of wire 1 =A

Area of wire 2 =3A

wire 1:

Y=F/AΔx/l---------(1)

wire 2:

Y=F′/AΔx/l/3-------------(2)

from (1) and (2)

FA×lΔx=F13A×l3Δx

F1=9F

Hence c is the correct answer.