# Homework Help: Physics 12 law or conservation of energy

1. Jun 28, 2013

### gdhillon

Q:A 46 g steel marble collides obliquely with an identical stationary marble, and continues
at 55 to its original direction. The collision is perfectly elastic. What is the angle between
the direction taken by the target ball and the original direction of the incident ball?

I know the collision being elastic means the kinetic energy is conserved, but I am completely lost on how to solve this question I tried drawing the vectors tip to tail but I didn't know how I would find theta because I don't know any of the sides.

2. Jun 28, 2013

### darkxponent

Two marbles and a ball? The problem is not clear.

3. Jun 28, 2013

### Staff: Mentor

What else is conserved in collisions? It's a vector quantity, so it must be conserved separately in any given direction (that means the x-component sums are conserved, and the y-component sums are conserved separately). Given equally massed projectiles, what does that tell you about the required symmetry of the resulting trajectories?