力　學　問　題

Total loss of potential energy = 60g x (10+3) J = 7800 J
Using work done = loss of potential energy
(F - 60g)x 3 = 7800
where F is the resistance of water, and (F-60g) is the net force acting on the man by the water.
i.e. F = (7800/3 + 60g) N = 3200 N

mg(H+h)=(friction)X(H+h)
(60)(10)(10+3)=(friction)X(10+3)
friction=600N