Question

Three spheres each of mass m are placed at the vertices of an equilateral triangle of side l. Each sphere is moving towards centroid with velocity v. After collision a comes to rest and b continues to move in the same direction with velocity v. Find the direction and magnitude of velocity of c after collision

Answer 1

according to law of conservation of linear momentum, when external force acts on the system of bodies equals zero, linear momentum of system remains constant.
e.g., initial momentum = final momentum

initially, all particles were at rest.
therefore, initial momentum , $p_i=0$

hence, in order to conserve the linear momentum, the velocity of particle C will be same as velocity of particle B but in opposite direction.

hence, C will move just opposite to B.