Question

When a metal wire elongates by hanging a load $Mg$ on it, the gravitational potential energy of mass $M$ decreases by $Mgl$. This energy appears.

• A. Half as elastic potential energy and half as thermal energy
• B. As elastic potential energy completely
• C. As thermal energy completely
• D. As kinetic energy of the load completely

Answer 1

The correct option is C As thermal energy completely

When a metal wire elongates by hanging a load $Mg$ on it, decrease in potential energy of the load $=Mgl$ where $L=$ elongation of metal wire, Elastic potential energy stored in stretched wire $=\frac{1}{2}\times Mgl$

Difference of $Mgl$ and $\frac{1}{2}Mgl$ appears a heat energy in stretched wire

$\therefore$ Energy appearing as heat $=Mgl-\frac{1}{2}Mgl=\frac{1}{2}Mgl$.