(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

You run a race with your friend. At first you each have the same kinetic energy, but then you find that she is beating you. When you increase your speed by 21%, you are running at the same speed she is. If your mass is 77 kg, what is her mass?

2. Relevant equations

K=1/2mv^2

3. The attempt at a solution

K(initial me)=1/2*77*.79v

K(initial friend)=1/2*mass*v

1/2*77*.79v=1/2*mass*v

the v's cancel out so the mass should be 30.415/.5 or 60.83 but this is not the right answer. Does anyone know what I did wrong?

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Kinetic Energy Speed Increase

**Physics Forums | Science Articles, Homework Help, Discussion**