Question

A bullet of mass 19.6 grams is fired with a speed of 318 meters per second toward a wood block of mass 269 grams initially at rest on a very smooth surface. What is the change in momentum of the bullet if it ricochets in the opposite direction with a speed of 298 meters per second? Answer must be in 3 significant digits.

Answer 1

The change in the momentum of the bullet can be expressed as,

$\Delta p=m(u-v)$

Finally, the bullet moves in the opposite direction therefore, final velocity is taken as negative.

Plug in the known values,

$\begin{gathered} \Delta p=(19.6\text{ g)(}\frac{1\text{ kg}}{1000\text{ g}})(318\text{ m/s-(-298 m/s))} \\ =(0.196\text{ kg)(616 m/s)} \\ \approx12.1\text{ kgm/s} \end{gathered}$

Thus, the change in the momentum of bullet is 12.1 kgm/s.