What force does the cushion apply to the puck?

Question

 A hockey player slaps a puck into a cushion, which brings the puck to rest. If the puck's initial velocity was +40 m/s and it has a mass of 170 g, what force does the cushion apply to the puck? Assume the cushion acts on the puck for 0.03 s and the surface that the puck slides on is frictionless.  

Answer 1

We can start with the kinematic equation for velocity:

v_f - v_i = at

Solve for a:

a = (v_f - v_i)/t

Since final velocity is 0,

a = (0 - 40m/s)/0.03s = -1,333 m/s²

So the opposite force is -ma or

0.17kg x 1,333m/s² = 227N