# Collisions

by pinkyjoshi65
Tags: collisions
 P: 263 A 1.0 kg magnetized air puck moving across a level table at 0.24 m/s approaches head-on a stationary, similarly magnetized air puck of mass 0.50 kg. If the "magnetic collision" is repulsive and perfectly elastic, determine: (a) the velocity of each puck after the collision (b) the velocity of both pucks at minimum separation (c) the total kinetic energy at minimum separation (d) the maximum potential energy stored in the magnetic force field during the collision For A) i simply used the conservation of momentum and KE and found the final velocities (1-dimensional) For B) I am not sure how to find th miniimum distance
 Mentor P: 40,243 Hint: When the pucks are as close to each other as they get, what's the relationship of their velocities?
 P: 263 uhh..i am not sure abt this..velocities become the same..?
Mentor
P: 40,243

## Collisions

 Quote by pinkyjoshi65 velocities become the same..?
Exactly! (If the velocities weren't the same, then they'd keep getting closer.) So figure out what that velocity must be.
 P: 263 so you are saying that the collision becomes the case of a perfectly inelastic collision...?
 P: 263 if thats the case, then M1v= (M1+M2)V hence V= M1v/M1+M2
 Mentor P: 40,243 Exactly.
 P: 263 ahh k..so for part c its quite staight foreward. we have to use0.5(M1+M2)V2 For part d potential enegy will be max when the h is max. How do we find the h..?
 P: 263 and also this is all 1-dimensional yes?
Mentor
P: 40,243
 Quote by pinkyjoshi65 ahh k..so for part c its quite staight foreward. we have to use0.5(M1+M2)V2
Right.
 For part d potential enegy will be max when the h is max. How do we find the h..?
What do you mean by "h is max"? Just use the fact that total energy is constant.

 Quote by pinkyjoshi65 and also this is all 1-dimensional yes?
 P: 263 so then the potential energy will be equal to the kE in part C)..?
Mentor
P: 40,243
 Quote by pinkyjoshi65 so then the potential energy will be equal to the kE in part C)..?
No, but the sum of PE + KE must be constant. (What's the initial total energy?)
 P: 263 initial total energy is M1v1^2+ M2v2^2
Mentor
P: 40,243
 Quote by pinkyjoshi65 initial total energy is M1v1^2+ M2v2^2
Not exactly. Initially, only one puck is moving. (And that's not the correct formula for KE!)
 P: 263 yes so M2v2^2 will 0..i know that hence the initial total energy will be 0.5*M1v1^2= 0.0288J. so then we can subtract the KE (from part c)frm this energy to find the PE
 Mentor P: 40,243 Now you've got it.

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