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Impact speed

  1. Oct 17, 2014 #1
    1. The problem statement, all variables and given/known data
    A ball is thrown toward a cliff of height h with a speed of 28.0 m/s and an angle of 60.0° above horizontal.
    What is the ball's impact speed

    2. Relevant equations
    Vf=Vi-at
    Sf=Si+Vit-1/2gt^2
    Vy=sintheta
    Vx=costheta

    3. The attempt at a solution
    first find the vertical velocity = 28 sin 60 = 24.25m/s

    find time to maximum height from Vf = Vi+ at
    0 = 24.25 - 9.8t
    t = 2.47sec

    the height reached
    v^2 = u^2 + 2as
    0 = 24.25^2 - 2 x 9.81 s
    s = 29.97m

    the ball must drop for 3.5 - 2.47 sec = 1.03s
    find the height it falls s = 1/2 at^2
    s = 0.5 x 9.8 x 1.03^2
    s = 5.2m

    the impact speed is 5.2m /1.03s= 5.05m/s
     
  2. jcsd
  3. Oct 17, 2014 #2

    BvU

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    Science Advisor
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    Gold Member

    Hi Hal, welcome to PF :-)

    Depends on whether the cliff is hit from aside or the ball lands beyond the top...

    :nb) or is there an extra given bit that you missed to render ? Like the 3.5 seconds that appear from somewhere ? What's the full problem statement ?

    Whatever, your last line uses an equation for average speed that cannot be applied for accelerated motion.

    FInally: what about the speed in horizontal direction ?
     
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