Energy Quiz Question?

[Victoria]

How fast do you need to launch an object upwards to make it reach a height of 75.5 m?

This was on an Energy quiz I had, but I don't know how to solve it. It was in the Knowledge section so it should be easy, but I just can't figure it out.

 

[sahil]

u must be knowing that the velocity becomes zero at the max. height. so put this formula... v^2 = 2gh.. here, v is the velocity u wanna find, g is gravity(9.8 m/s^2) and h is the max. height given in the question.
Hope it helps..

 

[PaulJackson]

The kinetic energy of the object when we launch it must equal the gravitational potential energy at the highest point.

mgh = mv^/2

gh = v^2/2

2gh = v^2

?(2gh) = v

g = 9.8 m/s^2

h = 75.5 m

?(2*9.8*75.5) = 38.5 m/s