A bullet of mass 15 g has a speed of 400 m/s. What is its kinetic energy? If the bullet strikes a thick target and is brought to rest in 2 cm, calculate the average net force acting on the bullet. What happens to the kinetic energy originally in the bullet?
Given,
Mass = 15g = 0.015kg,
Initial velocity = 400m/s,
Distance, s = 2cm = 0.02m
K.E. (initial) = 1/2mv2
= 1/2 x 0.015 x (400)2
K.E. (initial) = 1200J
As final velocity = 0.
Therefore, K.E. (final) = 0 (Where F is the average force)
F = 1200/2 × 10−2
= - 6 × 104 N
Negative sign shows that force is acting opposite to the direction of motion of the bullet. And the kinetic energy originally in the bullet is eventually transformed into heat energy by friction.