The magnitude of the magnetic field?

Question

An electron at point A in the figure View Figure has a speed of 1.48×10^6 m/s Find the magnitude of the magnetic field that will cause the electron to follow the semicircular path from A to B . This is the link to the picture http://session.masteringcollegephysics.com/problemAsset/1020007/3/20P18.jpg

I've tried using the equation R=(m*v)/(q *B) solving for B but it doesnt work i get the wrong answer 1.68×10^−6 using the mass of the electron 9.10938*10^-31 and its charge 1.602*10^-19 and radius 5 any ideas of what im doing wrong and what should i do? thanks.

I forgot to say that they are also asking me the time it would take to go from A to B. thanks.

Answer 1

First, at the speed this electron is going it's v << c so we can do a non-relativistic answer.

You've got the correct equation.

My calculation results in the following
B=(mv)/(qr)=(9.1E-31 kg)(1.48E6 m/s)/((1.6E-19 C)(0.05 m))

=1.7E-4 T into the paper