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