Q. A lead bullet of $10\ g$ travelling at $300\ m/s$ strikes against a block of wood and comes to rest. Assuming 50% of heat is absorbed by the bullet, the increase in its temperature is (specific heat of lead $= 150J/kg,K$)

A) $100℃$
B) $125℃$
C) $150℃$
D) $200℃$
Explanation

(c) Since specific heat of lead is given in $Joules,$ hence use $W = Q$ instead of $W = JQ.$
$\Rightarrow \frac{1}{2} \times \left( \frac{1}{2}mv^{2} \right) = m.c.\mathrm{\Delta}\theta \Rightarrow \mathrm{\Delta}\theta = \frac{v^{2}}{4c} = \frac{(300)^{2}}{4 \times 150} = 150℃$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.