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Mechanics
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PARTHESH BULBULE
Cool goIITian

Joined: 25 Jul 2007
Posts: 82
19 Sep 2007 18:58:56 IST
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Suppose m & M are two masses which are to be collided, and u1 & u2 are their initial velocities while v1 & v2 are their final velocities respectively.
Then according to the law of conservation of momentum,
mu1 + Mu2 = mv1 + Mv2
Newton's experimental law says that, If two bodies with initial speeds u1 & u2 collide, so they have final velocities v1 & v2 , then,
-e = v2 - v1/ u2 - u1
where e is the coefficient of restitution v2 - v1 is the velocity of seperation and u2 - u1 is the velocity of approach.
For example if two bodies with initial velocities 3m/s & 4m/s suffer a head-on collision then, and their final velocities are 1m/s and 5m/s then,
velocity of approach is 4 - 3 = 1m/s & velocity of seperation is 5 - 1 = 4m/s.
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19 Sep 2007 21:55:00 IST
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there is nothing great in its math. just understand basic cocept and U will never face any difficlty. Suppose U R running after a thief, Your velocity is Ui and thief's T. Then you are appraching thief with a net vlocity of Ui-T. With this resultant velocity you are approaching. Thus Ui-T is velocty of approach. But, just on catching him he slips and runs away at speed Tf and you are following him with velocity Uf, the thief is seperating from you with a resultant velocity of Tf-uf. (normally we assume, Tf is higher than Uf) . It is found in elastic collisions that ratio Tf-uf/Ui-T is 1. But if this ratio is less tha 1 , You can confidently declare it is not elastic collision. It will be inelastic collision.











