Mass of bullet = 25g = 0.025kg.
Mass of pendulum = 5kg.
The vertical displacement h = 10cm = 0.1m
Let it strike the pendulum with a velocity u.
Let the final velocity be v.
0 – (1/2) (M + m). V2 = – (M + m) g × h ⇒ u2/(201)2=2 × 10 × 0.1 = 2
⇒ u = 201 × √2 = 280 m/sec