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    So p=mv normally but why does p=2mv when a molecule or something hits a wall and comes back?
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    V is velocity and when using velocity direction matters so if a ball hits a wall with speed V and rebounds with same speed, the speed of rebound will be -V. Hence, the momentum changed from V to 0 and then from 0 to -V.
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    (Original post by Radioactivedecay)
    V is velocity and when using velocity direction matters so if a ball hits a wall with speed V and rebounds with same speed, the speed of rebound will be -V. Hence, the momentum changed from V to 0 and then from 0 to -V.
    I get that it will become -V because opposite direction but what do you mean by "the momentum changed from V to 0 and then from 0 to -V". How does that make the equation p=2mv?
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    (Original post by aceplayyt)
    I get that it will become -V because opposite direction but what do you mean by "the momentum changed from V to 0 and then from 0 to -V". How does that make the equation p=2mv?
    Sorry I meant to say that the speed, not the momentum, changes from V to -V. First, lets clear one thing, 2mv is not the momentum of the object, it's the change of momentum that occurred ie, the impulse given. Recalling the impulse equation: I=mv-mu, but since we defined a direction we get m (-V)-mu=-2mV, so the total change in momentum is 2mV
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    Momentum is a vector so has both magnitude and direction. This direction is indicated using a minus sign (-mv) just means mv in the opposite direction. The change is momentum is the final momentum minus the initial momentum
 
 
 

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