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Vertical motion question

  1. Jul 9, 2011 #1
    i got an assignment for physics and my class hasn't done alot of vertical motion yet, it sounds like a pretty traight forward question but im battling.

    A helicopter is rising vertically with a velocity of 14.7m/s when its wheel drops off at a height of 49m

    i) calculate the time for the wheel to reach the ground

    ii) what is the velocity of the wheel on impact with the ground

    im guessing when i find the time the velocity will be easy to find, the main thing im struggling to deal with, is the initial velocity 14.7m/s?
     
  2. jcsd
  3. Jul 9, 2011 #2

    tiny-tim

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    Welcome to PF!

    Hi Elviklemon! Welcome to PF! :wink:
    That's right! :smile:

    Since it isn't pushed (it only "drops off"), its velocity will be the same as that of the helicopter.​
     
  4. Jul 9, 2011 #3
    but in that case i have
    u = 14.7m/s
    s = 49m
    a = -9.8m/s^-2

    i cant find an equation that will find the time?
     
  5. Jul 9, 2011 #4

    tiny-tim

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    Hi Elviklemon! :smile:

    (try using the X2 icon just above the Reply box :wink:)
    Learn by heart all the standard https://www.physicsforums.com/library.php?do=view_item&itemid=204" equations …

    you need one beginning s = … :wink:
     
    Last edited by a moderator: Apr 26, 2017
  6. Jul 9, 2011 #5
    i dont know how to use the x^2 thing sorry :P ,

    would the S = a negative number? because it can only travel downwards?
     
  7. Jul 9, 2011 #6

    tiny-tim

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    if a is negative, then s = -49
     
  8. Jul 9, 2011 #7
    Thanks heaps mate, i think i've figured her out, now i just have 4 momentum questions to go before i hand it in to my teacher in 2 days time :/

    (and its great to be here at PF ;) )
     
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