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Homework Help: Marksman on a railroad car

  1. Oct 30, 2006 #1
    A marksman standing on a motionless railroad car fires a gun into the air at an angle of 30.0° from the horizontal (the figure below). The bullet has a speed of 175 m/s (relative to the ground) and a mass of 0.0110 kg. The man and car move to the left at a speed of 1.20 10−3 m/s after he shoots. What is the mass of the man and car?
    [Hint: A component of a system's momentum along an axis is conserved if the net external force acting on the system has no component along that axis.]


    I know that Pi = Pf where there is conservation of momentum.

    so M1V1i + M2V2i = M1V1f + M2V2f
    0 = M1V1f + M2V2f

    but I'm not sure what numbers to plug in because there is also an angle involved.
  2. jcsd
  3. Oct 30, 2006 #2
    Use the horizontal component of the bullet (it will involve a trig function [sin, cos, or tan] of the angle).
  4. Oct 30, 2006 #3
    thanks! i got the correct answer. :)
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