Case II – If Ra atom is having an uniform velocity before, then He and Rn can have complex trajectories but COM will have the same VELOCITY as of Ra atom.
Example- A bullet of mass m is fired at a velocity of v1, and embeds itself in a block of mass M, initially at rest and on a frictionless surface. What is the final velocity of the block?
Solution: Now if we take bullet and block as a system, then no external force is acting on it. So we can conserve momentum.( m1v1 + Mv2) before =( m1 + M) vafter
vafter = m1v1 /( m1 + M), as the initial velocity of block M is zero. Vector Product o
Vector product( cross product) of two vectors a and b is a × b = ab sinΘ = c, where Θ is angle between a & b
o Vector product c is perpendicular to the plane containing a and b. o
If you keep your palm in direction of vector a and curl your fingers to the direction a to b, your thumb will give you the direction of vector product c