Answer
a) The average force exerted on the goalie by the puck is $+2210N$.
b) The average force exerted on the goalie by the puck is $+4420N$.
The answers are consistent with the conclusion reached in Conceptual Example 3.
Work Step by Step
a) The impulse-momentum theorem states that $$\vec{F}\Delta t=m\vec{v}_f-m\vec{v}_0$$ $$\vec{F}=\frac{m\vec{v}_f-m\vec{v}_0}{\Delta t}=\frac{m}{\Delta t}(\vec{v}_f-\vec{v}_0)$$
We have the pucks's mass $m=0.17kg$, time $\Delta t=5\times10^{-3}s$, initial velocity $\vec{v}_0=+65m/s$; since the puck was caught, $\vec{v}_f=0$.
The force exerted on the puck by the goalie is
$$\vec{F_{gp}}=-2210N$$
According to Newton's 3rd law, the force the puck exerts on the goalie $\vec{F_{pg}}$ has the same magnitude but opposite direction, so $\vec{F_{pg}}=+2210N$.
b) Similarly, we still use the formula $$\vec{F}=\frac{m}{\Delta t}(\vec{v}_f-\vec{v}_0)$$
but now $\vec{v_f}=-65m/s$
The force exerted on the puck by the goalie is
$$\vec{F_{gp}}=-4420N$$
According to Newton's 3rd law, the force the puck exerts on the goalie $\vec{F_{pg}}$ has the same magnitude but opposite direction, so $\vec{F_{pg}}=+4420N$.
The force in b) has double the magnitude as the force in b), so the answers are consistent with the conclusion reached in Conceptual Example 3.
