Question

A 7.80 g bullet is initially moving at 560 m/s just before it penetrates a tree trunk to a depth of 5.60 cm.

(a) What is the magnitude of the average frictional force (in N) that is exerted on the bullet while it is moving through the tree trunk? Use work and energy considerations to obtain your answer.

(b) Assuming the frictional force is constant, how much time (in s) elapses between the moment the bullet enters the tree trunk and the moment it stops moving?

Answer 1

A)

Using work energy theorem,

Fd = 0.5 m (v^2 - u^2)

F x 0.056 = 0.5 x 0.0078 x 560^2

F = 2.18 x 10^4 N

B)

Displacement, d = (v/2) t

0.056 = (560/2) t

Time, t = 2 x 10^-4 sec

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