Question

Question:

A bullet of mass of 10 gram travelling horizontally with a velocity of 150 m/s strikes a stationary wooden block and comes to rest in 0.03 s. Calculate the distance of pentration of the bullet into the block also calculate the magnitude of the force exerted by the wooden block on the bullet.

In the answer, how did the force have positive acceleration??

Explain briefly..

Answer 1

No we are considering it as retardation and retarding force. if we are considering it as acceleration then it will be negative

Data:
mass of the bullet (m) = 10 g = (10/1000) kg =0.01 kg
Initial velocity (u) = 150 m/s
Final velocity (v) = 0 m/s
Time taken (t) = 0.03 sec

i. Calculation of the distance of penetrationof the bullet into the block:

Calculation of the distance of penetrationof the bullet into the block = Displacement

Displacement = average velocity × time
Displacement = [(u + v) / 2] × time
Displacement = [(150 + 0) / 2] × 0.03
Displacement = 2.25 m


ii. Calculation of the magnitude of the force exerted by the wooden block on the bullet:
the magnitude of the force exerted by the wooden block on the bullet = Retarding force
Retarding force = mass × reatardation
Retarding force = mass ×[ (Intitial velocity - Final velocity) / t ]
Retarding force = 0.01 ×[ (150 - 0) / 0.03 ] N
Retarding force = [150/3] N
Retarding force = 50 N