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Homework Help: Formula equations and momentum!

  1. Jul 17, 2004 #1
    hey again all!

    When given the following information, what equation do you use to solve this and should the answer be around .02 N?

    A superball (very bouncy) of mass .05 Kg is dropped onto a table top. Its speed as it hits the table top is 6.0 m/s. It bounces off the table and rises to the same height from which it fell. If the superball was in contact with the table for 30 ms (What is ms? is it a typo? i had trouble figuring that out too), calculate the average net force (magnitude and direction) exerted on the ball during its collision with the table. Show your work. (hint: calculate the change in momentum caused by its collision with the table.)

    For this problem, i said (with the given values):
    F = 0.5 Kg (6.0 - 6.0) / 30 ms? F = 0.02 N

    Is this correct? is it even int he right ballpark? Please help me and leave me any advice you can :redface:

    Thank you
  2. jcsd
  3. Jul 17, 2004 #2


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    Okay, first "ms" is milliseconds or [tex]10^{-3}[/tex] seconds.

    Then I think you mean to say F = 0.5 Kg (6.0 - (-6.0))m/s / 30 ms .

    This is correct, and should give you the answer F = 200 N
  4. Jul 18, 2004 #3
    0.5 or 0.05? A 0.5 kg superball is unrealistic. A 0.05 kg superball is a little more realistic, but still too small since that is the mass of only five Cheez-It crackers (which are scientifically manufactured to produce masses of EXACTLY one gram each).
  5. Jul 18, 2004 #4
    hey, you must be in my physics class cause we have the same homework questions! Anyways, i got 2N because 30 milliseconds is .3 of a second. so you have to divide it by .3 instead of 30.
  6. Jul 19, 2004 #5
    30 milliseconds is 0.03 seconds.
  7. Jul 19, 2004 #6
    uh oh... then what is 1 of those things on the stopwatch?
  8. Jul 19, 2004 #7


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    centiseconds ?
  9. Jul 19, 2004 #8
    Princexcharles....1000 ms is equal to 1 second....so 30 ms would be 0.03 seconds.

    Also, Physicsneededhelp...for future reference, make sure you check your units before you go through with your calculations. In your earlier post, you were dividing meters/seconds by miliseconds....make sure all your units are the same (i.e...in the case of the problem above, because velocity was expressed in m/seconds....your time should also be expressed in seconds.) Keep this in mind, and it should make everything a lot easier!! :-D
  10. Jul 19, 2004 #9
    what's a "short circuit"? (general physics, please help!!)

    I am currently reading electricity and although I have read my textbooks well, I still dont understand what a "short circuit" is..thanks
  11. Jul 19, 2004 #10


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    How did this get into a thread on "Formula equations and momentum!"?
    (As a matter of courtesy- start your own thread, don't hijack others.)

    A "short circuit" is exactly what it says: two of the wires accidently cross so that the circuit is shorter than it should be (imagine a circle squeezed into a figure 8).
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