Question

2. In a ballistics demonstration a police officer fires a
bullet of mass 20g with speed 100ms 2 on soft
plywood of thickness 2.00 cm. the bullet emerges
with only 10% of its initial kinetic energy. What is
the emergent speed of the bullet?​

Answer 1

Answer:

Here, m=50.0g

=501000kg=120kg

vi=200ms−1

∴ Initial K.E., Ki=12mv2i

=12×120(200)2=1000J

Final K.E., Kf=10%(Ki)

=10100×1000J=100J

If vf is emergent speed of the bullet, then

12mv2f=Kf

vf=2Kfm−−−−√=2×1001/20−−−−−−−√=63.2m/s

Note that K.E. is reduced by 90% but speed is reduced by nearly 68%.