Question

a bullet of mass 100 gm ,moving with a velocity of 200m/s,strikes a wall and comes to rest .what is the work done by the wall on the bullet ?if the bullet penetrates the wall to a depth of 1 cm.what is the average retarding force exerted by the wall on the bullet

Answer 1

Here,

Mass, m = 100 g = 0.1 kg

Initial velocity, u = 200 m/s

Distance, s = 1 cm = 0.01 m

Using,

v² = u² + 2as

=> 0 = 200² + 2a(0.01)

=> a = -2000000 m/s²

Negative sign implies retardation.

So, force by the wall on the bullet is, F = ma = (0.1)(-2000000) = -200000 N

Negative sign implies force is opposite to the direction of motion of bullet.

So, work done by wall on bullet = Fs = (-200000)(0.01) = -2000 J

Negative sign comes because force by the bullet and the displacement of the bullet are in opposite direction.