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Homework Help: Bullet Lodges In Baseball (vertical)

  1. Apr 9, 2009 #1
    1. The problem statement, all variables and given/known data

    A 0.028 kg bullet is fired vertically at 185 m/s into a 0.15 kg baseball that is initially at rest. The bullet lodges in the baseball and, after the collision, the baseball/ bullet rise to a height of 37 m.

    (a) What was the speed of the baseball/bullet right after the collision?

    (b) What was the average force of air resistance while the baseball/bullet was rising? (Consider the positive direction to be upwards.)

    2. Relevant equations

    conservation of momentum.

    3. The attempt at a solution

    m1v1=m2v2 yeilding v2 (velocity of ball/bullet combo) of 29.1 m/s.
    This was correct.

    However, I can't figure out b.

    I tried using Force of Air Resistance = KE - PE, but that doesn't work.

    I also tried using Force Air Resitance =KE/h - m(total)-g

    That didn't work either (found it on yahoo answers).

    What am I missing here?
  2. jcsd
  3. Apr 9, 2009 #2


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    I think you need to consider that KE = PE_final + W_air


    W_air = AvgForce_air * distance.
  4. Apr 9, 2009 #3
    Yes, but I still don't get the right answer even then:

    KE = PE_final + W_air

    Thus, W_air = KE - PE

    Wair = ((.5)(.178)(29.1^2)) - ((.178)(9.8)(37)) = 75.366-64.543 = 10.823


    W_air = AvgForce_air * distance


    AvgForce_air = w_air / distance

    AvgForce_air = 10.823 / 37 = 0.293 (which isn't accepted)

  5. Apr 10, 2009 #4


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    Look at it another way.

    Your initial velocity is 29.1.

    Figure acceleration against the upward motion.

    V2 = 2*a*x

    a = 29.12/(2*37) = 11.44 m/s2

    Well you know g was 9.8 so you apparently had an additional force that affected a 1.64 m/s2 downward drag.

    1.64*.178 = ... oops ... looks like .293N again.
  6. Apr 10, 2009 #5
    So im still confused?
  7. Apr 10, 2009 #6


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    Or maybe .293 is correct?
  8. Apr 10, 2009 #7
    http://dl.getdropbox.com/u/119186/Picture%201.png [Broken]
    Last edited by a moderator: May 4, 2017
  9. Apr 10, 2009 #8
    Webassign sucks...this is for practice and it gives no feedback as to what we may be doing wrong...
  10. Apr 10, 2009 #9


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    They want -.293 I think. The force is against the direction of motion which is up.
    Last edited by a moderator: May 4, 2017
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