# The length of a rod is 40 cm and area of cross-section 4 cm2 . The Young’s modulus of the material of wire is 4 x 1010 NM-2.

The length of a rod is 40 cm and area of cross-section 4 cm2 . The Young’s modulus of the material of wire is 4 x 1010 NM-2. If the rod is compressed by 10 kg-wt along its length then increase in the energy of the rod in joules will be(a) 8.57 x 10-6 J(b) 2.36 x 10-4 J(c) 1.25 x 10-3 J(d) 1.25 x 10-4 J

Answer is : (d) - 1.25 x 10 -4 J Energy  $$=\frac{1}{2}FI=\frac{1}{2}\frac{F^2L}{AY}$$   $$\left[\because Y=\frac{FL}{AI}\right]$$ $$=\frac{1}{2}\times \frac{(100)^2\times 40\times 10^{-2}}{4\times 10^{-4}\times 4\times 10^{10}}$$ = - 1.25 x 10 -4 J