A 10 g bullet moving at 370 m/s strikes a ballistic pendulum of mass 2kg. The bullet emerges with a speed of 100 m/s.

What height does the pendulum rise to?

I don't want the answer, i just need hints!!! thnaks

1 answer

Use conservation of linear momentum to compute the speed V of the bob of the pendulu immediatly after impact. Neglect mass loss.
0.01*370 = 0.01*100 + 2.0*V
Solve for V.
V = 0.005*(270) = 1.35 m/s

Then, use conservation of mechanical (kinetic + potential) energy to compute how high it swings (H).
M g H = (1/2) M V^2
H = V^2/(2g)

Mechanical energy is not conserved in the bullet-penetration process, but is during the free swing afterwards. Momentum is ALWAYS conserved when there are no outside forces.