A bullet having a mass of 10 g and moving with a speed of 1.5 ms−1, penetrates a thick wooden plank of mass 90 g. The plank was initially at rest. The bullet gets embedded in the plank and both move together. Determine their velocity.
The correct option is C. 0.15 ms−1.
Given,
the mass of bullet m1=10 g=0.01 kg,
initial speed of bullet u1=1.5 ms−1,
mass of wooden plank m2=90 g=0.09 kg,
final velocity of plank + bullet = v and
initial speed of wooden plank u2=0
Here, we apply the law of conservation of momentum, i.e., Final momentum = Initial momentum.
m1u1+m2u2=m1v+m2v
0.01×1.5+0.09×0=0.01×v+0.09×v
0.015=0.1v
On solving v=0.15 ms−1.