Q: A lead bullet of mass 21 g travelling at a speed of 100 ms-1 comes to rest in a wooden block. If no heat is taken away by the wood, then find the raise in temperature of the wood. (specific heat of lead = 0.03 calorie/g°C.)

Sol: kinetic energy of the bullet = heat gained by the bullet,

$\large \frac{1}{2} m v^2 = m s \Delta T$

$\large \Delta T = \frac{v^2}{2 s}$

$\large \Delta T = \frac{(100)^2}{2 \times 0.03 \times 4.2 \times 1000}$

= 39.68°C