Question

A Body with a mass of 150kg is located at a height of 45 m. If allowed to fell freely to the ground. What will be its velocity on impact?
KE= 1/2*m*v^2
PE= m*g*h
1/2*m*v^2= m*g*h
1/2*150kg*45m*v^2= 150kg*9.81*45m
3375* v^2= 66217.5
3375*v^2/3375= 66217.5/3375
v^2= 19.62m/s
Is this done correctly?

Answer 1

There are a lot more steps than you need.

V = sqrt(2 g h)
Forget about the mass.
I do not agree with your V^2 number. You have 45 meter height terms on both sides of your equation. That is wrong.

Answer 2

You have to use both potential energy and kinetic energy formulas since they are mutually convertible.

potential energy= mass(150) x gravity(9.81) x height(45m)
=66,217.5

plug that number into the following equation...

ke= 1/2 x mass x velocity^2

*remember pe = ke

66,217.5= 1/2 x 150 x v^2
132435=150 x v^2
882.9=v^2
29.713=v

the velocity will be 29.71 when the rock hits the floor. Utilize both formulas :)