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Homework Help: Conservation of momentum with sprins

  1. Apr 23, 2013 #1
    1. The problem statement, all variables and given/known data
    Problem 2 (35 points): A projectile of mass mA=20g is shot towards a block of mass
    MB= 5kg with a velocity of vA=400m/s. The block is at rest, attached to a horizontal
    massless spring (at equilibrium) with k=500N/m.

    a. If the collision between the projectile and the mass is perfectly elastic,
    what are the velocities of the two masses immediately following the collision?

    2. Relevant equations

    Conservation of momentum
    M1U1 + M2U2 = M1V1 + M2V2
    When U is equal to the velocity before the impact.

    3. The attempt at a solution

    I would have a good idea on how to do this problem without the spring being there but with it there i can not figure out how to do it.

    I know that the total velocities after the collision needs to combine to make 400 but other than that i am pretty lost on this one.
  2. jcsd
  3. Apr 23, 2013 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The spring is there to confuse you. Immediately after impact, how far has the spring compressed? What, then, is the force in it?
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