1. The problem statement, all variables and given/known data "A metal ball of mass 0.50 kg is dropped from the top of a vertical cliff of height 90m. When it hits the beach below it penetrates at a depth of 6.0cm. Calculate: a) the velocity of the ball just as it hits the sand b) the (average) retarding force of the sand 2. Relevant equations SUVAT equation: v2=u2+2as Newton's Second Law: F=ma 3. The attempt at a solution For part a) I used suvat (s=90m, u=0ms-1, v=v ,a=9.81ms-2 , t=t) and used the suvat equation to calculate the final velocity as 42ms-1 For part b) I am unsure, do I just use F=ma (with m=0.50kg and a=9.81ms-2) to get an answer of 4.91N, or am I missing something?