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

Answer 1

Answer: (C)

half as elastic potential energy and half as thermal energy

Answer 2

When a metal wire elongates by hanging a load $Mg$ on it, decrease in potential energy of the load $=Mgl$ (where $l=$ elongation in metal wire) Elastic potential energy stored in stretched wire $=\frac{1}{2}\times Mgl$ Difference of $Mgl$ and $\frac{1}{2}Mgl$ appears as heat energy in the stretched wire. $\therefore$ Energy appearing as heat $=Mgl-\frac{1}{2}Mgl$ $=\frac{1}{2}Mgl$