8.3 Exercise 15

Using energy considerations and assuming negligible air resistance, show that a rock thrown from a bridge 20.0 m above water with an initial speed of 15.0 m/s strikes the water with a speed of 24.8 m/s independent of the direction thrown. (Hint: show that $K_{\text{i}} + U_{\text{i}} = K_{\text{f}} + U_{\text{f}} \left.\right)$