# Kinetic energy efficiency question

1. May 7, 2013

### 13physicsdude

1. The problem statement, all variables and given/known data

A roller coaster descends 55m from the top of the first high point to the first low point in the track. The roller coaster converts gravitational potential energy to kinetic energy with an efficiency of 50.0%. What is the velocity of the roller coaster at the bottom of the first low point?

2. Relevant equations

Efficiency= (Eout/Ein)100%

3. The attempt at a solution

I have no clue how to do it!! I dont understand how to use the efficiency equation to get velocity, please help!

Last edited: May 7, 2013
2. May 7, 2013

### rock.freak667

You forgot to fill out this part, you'll need to before we can help you

3. May 8, 2013

### anjelin

Ein is gravitational potential energy, Eout is kinetic energy. Take into account the formula for kinetic energy, mv^2/2.

4. May 9, 2013

### Arkavo

then .5mgh=.5mv^2 then v=(gh)^(.5) solve to get

5. May 9, 2013

### Ashu2912

Using conservation of energy, the energy of roller coaster+earth system is conserved, in an ideal case, i.e. change in potential energy = change in kinetic energy. However, in this case there is 50% loss of energy, i.e. only half of the potential energy change equals the kinetic energy change. I think you have your answer now!! :)