Energy COE - Bullet in tree trunk, find the frictional force in stopping the bullet

Answer: Option C

With first glance, we may think of using kinematics to solve. It can, but the process will be longer. Refer to the video towards the end.

For such questions, it will be much easier to use conservation of energy (COE).

Besides the usually equating KE to GPE, we must not forget that we can also equate KE to WD. All are energy.