Question
Physics Question on work, energy and power
A simple pendulum of length 1 m has a wooden bob of mass 1kg . It is struck by a bullet of mass 10−2kg moving with a speed of 2×102ms−1 . The height to which the bob rises before swinging back is (Take g=10ms−2 )
A
0.2m
B
0.6m
C
8m
D
1m
Answer
0.2m
Explanation
Solution
Momentum of bullet =10−2×2×102=2kgms−1 . Let the combined velocity of the bob + bullet =v . Momentum of bob + bullet =(10−2+1)v=1.01v . By conservation of momentum, 1.01v=2kgms−1 or v=1.012=1.98ms−1 . By conservation of energy 21(M+m)v2=(M+m)gh or =h=2gv2=2×10(1.98)2 =0.19≃0.2m