Using energy considerations Since Ef=Ei, a rock thrown from the tip of a bridge doesn't matter which direction it is thrown in.
Given that,
Height of the bridge is 20m
Initial before he throws the rock
The height is hi = 20 m
Then, final height hitting the water
hf = 0 m
Initial speed the rock is throw
Vi = 15m/s
The speed at final is at which the rock hits the water
Vf = 24.8 m/s
Using given energy conservation
Ki + Ui = Kf + Uf
Where
Ki is initial kinetic energy
Ui is initial potential energy
Kf is final kinetic energy
Uf is final potential energy
Then,
Ki + Ui = Kf + Uf
Where
Ei = Ki + Ui
Where Ei is initial energy
E i =1/2mVi² +m*g*hi
E i =1/2m × 15² + m *9.8*20
E i = 112.5m + 196m
E i = 308.5m J
Now,
E f = Kf + Uf
E f =1/2mVf² + m*g*hf
E f =1/2m*24.8² + m*9.8* 0
E f = 307.52m + 0
E f = 307.52m J
Learn more about energy here:
https://brainly.com/question/9615089
#SPJ4
