# Magnetisim Problem! Just need an Equation.

1. Mar 2, 2005

### Fused

Here's the problem:

A proton follows a spiral path through a gas in a magnetic field of 0.010 T, perpendicular ot hte plane of the spiral. In two successive loops at points P and Q, the radii are 1.0 mm and 8.5 mm respectively. Calcualte hte hcnage in the kinetic energy of hte proton as it travels from P to Q/

I just need a general direction to go in and maybe what formulas to use. Since we are trying to find kinetic energy, would I be using the (mv)^2/r for centripetal force?

2. Mar 2, 2005

### stunner5000pt

Since the measured radii are iven you can assume taht the proton moved inb perfect circles given those radii.

so since it is moving in a perfect circle the centripetal force = magnetic force
$$m \frac{v^2}{r} = qvB sin \theta$$
where theta is the angle between the particle and the field (given to you)

solve for the unknown in that equation each time then find the change in kinetic energy