Question

A bullet moving with a velocity of 75 m/s is fired into the trunk of wood through which it penetrates 25 cm. If a bullet of same velocity were fired into a smaller piece of wood 10 cm thick with what velocity would it emerge assuming the resistence to be uniform?

Answer 1

The wooden trunk exerts a force (assumed constant) on the the bullet.

v = 0. u=75m/s. s = 0.25 m
v^2 = u^2 + 2 a s.
a = - 75^2/0.5 m/s^2

Now s = 10cm = 0.1m. a and u are the same.
v^2 = u^2 + 2 a s
= 75^2 - 2* 75^2 /0.5 * 0.1
= 0.6 * 75*75
v = 75 * sqrt(0.6) m/s

Answer 2

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