Question

A high diver of mass 52 kg jumps off a board 11 m above the water. If, 4.7 s after entering the water his downward motion is stopped, what average upward force did the water exert?

Answer 1

(average force)*(time underwater) = (momentum change)

The Kinetic Energy entering the water was

KE = M g H = 5606 J

V (entering water) = sqrt(2*KE/m) = 14.7 m/s

Momentum change under water (at lowest depth) = M*V = 764 kg m/s

Now divide by the 4.7 s for the average force in Newtons

Answer 2

162.533N