A 0.45-kilogram football traveling at a speed of 22 meters per second is caught by an 84-kilogram stationary receiver. if the football comes to rest in the receiver's arms, the magnitude of the impulse imparted to the receiver by the ball is

Impulse = Change in momentum.

The ball was moving with a momentum of 0.45 * 22 = 9.9

The ball comes to rest in the receivers arm; this means the ball's final velocity = 0. So mv2 = 0.45 * 0

The magnitude of the impact is just the change in momentum. 9.9 - (0.45 * 0) = 9.9