A man runs with a speed of 6 m/s off a platform that is 10m above the water. How fast is he moving when he heats the water

Free fall over 10m:

mgh = (1/2)mv²
v = √(2gh)
=2*9.81*10
=14 m/s
Horiz.velocity = 6m/s
Resultant velocity
= √(6²+14²)
= 15.24 m/s