SOMEONE ASKED ๐
How fast will he be moving backward just after releasing the ball?
HERE THE ANSWERS ๐

It depends on whether he puts his back and shoulders into it.
For the basic conservation principle:
85 kg * x + 0.43 kg * 13 m/s = 0
Solve for x.
HOWEVER…
If he put his back and shoulders into it, some of the force could be coming from torque through twisting of the torso which does not generate any horizontal motion..
Source(s): I just love screwing up teacher’s word problems! 
US football with Australian metric weights and distances …. Don’t you just love lazy aussie teachers?
if someone actually experiments with it, the upper torso moves backwards while the legs move forwards. It is a very poor example to get the mathamatical answer the teacher has at the back of his book

conservation of momentum. the momentum before = momentum after. momentum = mass x velocity.
m1v1 = m2v2.
the momentum of the ball going away from him will be equal in magnitude but opposite in direction to the player’s momentum.
the ball’s momentum is 0.43×13 Kgms^1 = 5.59Kgms^1.
so, he must also have this momentum.
you divide this momentum by his mass to get his velocity:
5.59Kg ms^1 / 85Kg = 0.066 ms^1.
this seems like a sensible answer.
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