(a) +9.30 kg m/s
The impulse exerted on an object is equal to its change in momentum:
where
m is the mass of the object
is the change in velocity of the object, with
v = final velocity
u = initial velocity
For the volleyball in this problem:
m = 0.272 kg
u = -12.6 m/s
v = +21.6 m/s
So the impulse is
(b) 155 N
The impulse can also be rewritten as
where
F is the force exerted on the volleyball (which is equal and opposite to the force exerted by the volleyball on the fist of the player, according to Newton's third law)
is the duration of the collision
In this situation, we have
So we can re-arrange the equation to find the magnitude of the average force: