isn't c option incomplete
v1 + v2 is parallwl to what ?
A nucleus moving wid a vel. v emits @(alpha) particle .Let the velocities of the @ particle nd the remaining nucleus be v1 nd v2 nd their massess be m1 nd m2 ....
(A)v,v1 nd v2 must be parallell to each other...
(B)none of the two v,v1 nd v2 should be parallell to each other....
(C)v1+v2 must be parallell to v.............
(D) m1v1+m2v2 must be parallell to v.......
D)
since momentum should be conserved then
(m_{1}+m_{2})\vec{V}= m_{1}\vec{v_{1}}+ m_{2}\vec{v_{2}}
thus m_{1}\vec{v_{1}}+ m_{2}\vec{v_{2}} is parallel to \vec{V}