Argh. Weirdly, I was able to get the correct solutions to the last two parts. However, the answer I had for part d was incorrect even though, I had to use it for the other parts.
Using r=mv/qB, B=mv/qr. m=0.0012 kg, v= 5 m/s, q=50e-5 C, r=0.3 m. B=400T?
I am confident this is correct. Is there...