# When an $\alpha$-particle of mass 'm' moving with velocity 'v' bombards on a heavy nucleus of charge 'Ze', its distance of closest approach from the nucleus depends on m as :
( A ) $\frac{1}{m^2}$
( B ) $\frac{1}{m}$
( C ) $\frac{1}{\sqrt{m}}$
( D ) $m$