Question

Two particles of the same mass have an elastic collision, the target particle being initially at rest. If it were not head on collision, the two particles move after collision
A. Parallel to each other
B. Anti-parallel to each other
C. Perpendicular to each other
D. Making an angle $120$

Answer 1

To solve this question we have to know that when two balls have equal mass, equal speed and when they collide with one another, the total linear momentum of the system becomes zero.

Complete answer:
We have to make our coordinate axis which should be one is along the line joining the centers of the two just at time on collision and one, tangential. Now, we have to consider the velocity of the moving ball which will come in two components of the coordinate axis. Here we are assuming ${v_n}$ as velocity normal and ${v_t}$ as velocity in tangential direction.

For collision we can say, the tangential part cannot change as there is no impact along that direction. A collision along normal is like a collision in one D. we know that the first particle has no velocity along normal and the second particle will go along normal.

So, the right answer will be option C.

Note: We can get confused between two velocities of tangential and normal positions. So, we have to know what is tangential velocity and what is normal velocity. Then only we will solve every question effortlessly.