Aprojectile (mass = 0.15 kg) is fired at and embeds itself in a stationary target (mass = 2.44 kg). with what percentage of the projectile's incident kinetic energy does the target (with the projectile in it) fly off after being struck?

38.6 %

Explanation:

First of all, we have to calculate the final velocity of the block-bullet system. We can apply the law of conservation of momentum:

where

m = 0.15 kg is the mass of the bullet

u is the initial velocity of the bullet

M = 2.44 kg is the mass of the block

U = 0 is the initial velocity of the block (it is at rest)

v is the final velocity of the bullet+block

Solving for v,

The total initial kinetic energy of the system is just the kinetic energy of the bullet:

While the final kinetic energy of the block+bullet is:

So the fraction of kinetic energy lost is

And so, the fraction of kinetic energy left in the projectile after he flies off the block is

1 - 0.614 = 0.386 = 38.6 %

we need to know the time interval during which the force acts. impulse of force = momentum change