
William W. answered 11/11/19
Experienced Tutor and Retired Engineer
You don't say so but I'm assuming the initial velocity was horizontal. This is a critical part of the problem but I'll go with that assumption.
In the horizontal direction, at 10 m/s the horizontal velocity doesn't change throughout the dive because the only force on the diver is the force of gravity acting in the y direction. So the time it takes the diver to go 48 m is (48 m)/(10m/s) = 4.8 s.
Now, looking at the y-direction, the distance y = viyt + 1/2at2 but viy = 0 (based on the initial assumption that the diver dove straight out in the horizontal direction) so y = 1/2at2 = 1/2(-9.81)(4.8)2 = -113.0 m