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 Jan 9th 2018, 09:35 AM #1 Banned   Join Date: Dec 2017 Location: Columbus Junction Posts: 5 Physics Homework Help Hi, I need a solution for my homework task but I still need help and explanation. On an ice skating rink, a girl of mass 50 kg stands stationary, face to face with a boy of mass 80 kg. The children push off of one another, and the boy moves away with a velocity of +3 m/s. What is the final velocity of the girl? –1.9 m/s +1.9 m/s –4.8 m/s +4.8 m/s Please, give me some explanation, not only the answer. Last edited by topsquark; Jan 13th 2018 at 03:56 PM.
 Jan 9th 2018, 11:12 AM #2 Senior Member     Join Date: Jun 2016 Location: England Posts: 366 The Total momentum (which is mass times velocity) remains constant. Note that in this case the total momentum is zero. This works out OK because the (final) velocities of the children are of opposite sign (one is positive and the other negative) so: BoyMass * BoyVelocity = minus GirlMass * GirlVelocity so: 80*3 = - 50*? Another (equivalent) way of viewing this is that the final velocities will be apportioned according to the two masses (the lighter mass ending up going faster) __________________ ~\o/~ Last edited by Woody; Jan 9th 2018 at 11:16 AM.

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