# Impact Speed

1. Feb 23, 2009

### redbutterfly

1. The problem statement, all variables and given/known data
Using energy conservation and assuming negligible air resistance, calculate the impact speed of a 4.00 kg cannon ball after being dropped from a height of 55.0 m.

2. Relevant equations
KE sub total=KE sub 1+KE sub 2
speed=distance/time
gravity=9.8

3. The attempt at a solution

2. Feb 23, 2009

### Delphi51

Welcome to the physics forums! Hope you ask lots of questions here.

As the ball drops, its gravitational potential energy is converted to kinetic energy. Start with:
Potential energy at the top = kinetic energy at the bottom

Fill in the detailed formulas, solve for the quantity you want to find, then put in the numbers you know.

3. Feb 23, 2009

### redbutterfly

Thank you!

TE=KE+PE sub g
PE sub g=mgh
PE sub g=4*9.8*55=2200 J
KE=0
TE=0+2200
2200=KE+0
KE=2200=1/2*4*v^2
4400=4*v^2
1100=v^2
v=33 m/s

4. Feb 23, 2009

### Delphi51

That's it!
Maybe simpler to write mgh = 1/2m*v^2, cancel the m's, then solve for v:
v = sqrt(2gh) = sqrt(2*g*55) = 32.8 m/s