# Homework Help: 2 bullets fired at the same time - find kinetic energies

1. Dec 9, 2008

### nn3568

1. The problem statement, all variables and given/known data
Two bullets have masses of 4.7 g and 11 g, respectively. Each is fired with a speed of 39.0 m/s.
a) What is the kinetic energy of the first bullet? Answer in units of J.
b) What is the kinetic energy of the second bullet? Answer in units of J.
c) What is the ratio K2/K1 of their kinetic energies?

2. Relevant equations
KE = 1/2 mv2

3. The attempt at a solution
KE = 1/2 * 4.7g * (39.02 m/s)
and so on...

However, I do not know why the site is telling me my answers are wrong!

2. Dec 9, 2008

### alphysicist

Hi nn3568,

Did you convert the mass units to kg before entering the answer (if you leave it in grams the answer will not be in joules)? If so, what did you get?

3. Dec 9, 2008

### nn3568

Yes, I did convert it into kg when I did the problem again but the site still said I was wrong :(

3574.35 (w/o changing to kg)
1.833 (no idea)
35.7435 (change to kg)
0.01 (from a bad source :( )

4. Dec 9, 2008

### nn3568

OH i get what i did wrong. i messed up in converting!

5. Dec 9, 2008