The net force on him when the elevator is accelerating up is 45N up. That's what accelerates HIM up.
I believe this is it
The centripetal force is given by
F = mv^2 / r
When v' = v/2,
F' = mv'^2/r = m(v/2)^2/r = mv^2/4r = F/4.
So the centripetal force is divided by 4.
Total Mechanical Energy = KE + PE
KE = (1/2)mv²
= (1/2)*8*20² = 1600 J
PE = mgh g ≈ 10 m/s²
= 8 * 10 * 85 = 6800J
Total Mechanical = 1600 + 6800 = 8400 J.