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## Homework Statement

A proton (mass= 1.67×10-27 kg, charge= 1.6×10-19 C) traveling with speed 1×106 m/s enters a region of space containing a uniform magnetic field of 1.2 T.

The magnetic field is coming out of the screen.

What is the time t required for the proton to re-emerge into the field-free region?

## Homework Equations

qvB = mv

^{2}/R

## The Attempt at a Solution

I begin by solving for R using the above equation:

R= (mv)/(qB)

Since the proton moves in and then back out it completes a semi-circle. The distance traveled is then πR as it is half of the circumference of a circle.

The velocity does not change for the entire distance traveled so dividing distance by velocity should give me the time.

This comes out as incorrect though. I am unsure as to what I am doing wrong.