# Homework Help: In 1/2mv^2, is m grams & v ft per second?

1. Sep 1, 2006

### skizbok

I understand that the energy is in joules (?), but unsure of mass and velocity formats. Im trying to calculate the energy of an impact. Specifically, the heat energy (btu) resulting from various bullet impacts. Feel free to ask further questions if you need to know something else to answer my question.

Thank you

2. Sep 1, 2006

### d_leet

To get an answer in joules, m must be measured in kilograms, and v in meters per second.

3. Sep 1, 2006

### Andrew Mason

The energy of a bullet of mass m travelling at speed v is $E = \frac{1}{2}mv^2$

Assuming that this is all converted to heat on impact, the heat produced is:

$$Q = E = \frac{1}{2}mv^2$$

Life is too short to use British units. Put the units in MKS (metres, kg, sec.) and then convert at the end if you want Btu. 1 Btu = 1055 J.

AM

4. Sep 2, 2006

### skizbok

Thank you. PS - I like your thoughts on British units :)