# Homework Help: More impulse and restitution >.<

1. Apr 9, 2004

### BananaMan

God i hate this damned topic >.<

Q. Two particles P and Q have speeds of 6m/s and 0m/s respectively. P directly collides with Q, the colision is perfectly elastic.

a) find the speed of Q directly after impact
b) find the impulse on Q

a)
so far i have worked out that using the law of conservation of momentum that

6 = X + 0.5Y

where x and y are the velocities of P and Q after the collision respectivly

however this is as far as i have got because to work out n e thing more i would need the coefficient of restitution

6 = E (X - Y)

b) would be easy given the velocity after :P

2. Apr 9, 2004

### himanshu121

e=1 for perfectly elastic Collision

3. Apr 9, 2004

### The_Brain

perfectly elastic collision

examples of a perfectly elastic collision (although they can never truly happen) would be a tennis ball that returns to its initial height after it is dropped or 2 billiards balls that collide and they exchange velocities. this should help get you started.

4. Apr 9, 2004

### HallsofIvy

We would appreciate it if you would include ALL of the information in a problem (better: quote it exactly) rather than making us guess. I take it from "6= X+ 0.5Y" that P has mass 1 kg and Q has mass 0.5 kg but I don't see that information anywhere in the problem. Since this is a "perfectly elastic" collision, you also have conservation of kinetic energy (same thing: the "coefficient of restitution" is 1). Assuming P has mass 1 kg and Q has mass 1/2 kg then the total kinetic energy (1/2)(1)(62)= (1/2)(1)X2+ (1/2)(1/2)Y2 or 36= X2+ (1/2)Y2. That equation, together with X+ (1/2)Y= 6 is enough to solve for X and Y.

5. Apr 9, 2004

### BananaMan

sorry was sleepy wen i posted it