Two protons, moving in a plane perpendicular to a uniform magnetic field of 500 x 10-4 T undergo an elastic head-on collision. How much time elapses before they collide again?

Question

anonymous · Answer

if they come from opposite directions and collide, they'd be continuously acted upon by the firce due to the magnetic field and will perform a circular motion

anonymous · Answer

so,
$$qvB={m_pv^2\over r}\
qB=m_p{v\over r}\
{qB\over m_p}={r\omega\over r}\
{qB\over m_p}=\omega={2\pi\over T}\
\Large T={2\pi m_p\over qB}
$$

anonymous · Answer

ohh, great, now i got it, thx

anonymous · Answer

yw