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Kinematics Question: Falling object

  1. Apr 16, 2017 #1
    1. The problem statement, all variables and given/known data
    Marian, who is standing on her balcony, is surprised by a pigeon and throws a flowerpot up in the air at 2.1 m/s. It takes 3.0 s for the flowerpot to smash to the ground. The flowerpot experiences acceleration due to gravity of 9.81 m/s [down].

    a) How high is Marian’s balcony?

    b) How fast was the flowerpot moving just before it smashed to the ground?

    2. Relevant equations
    For a) I believe I"m using ##\vec d = v_1 \Delta t + \frac 1 2 \vec a \Delta t^2##

    for b) ##\vec v_2 = \vec v_1 + \vec a \Delta t##

    3. The attempt at a solution
    a) ##\vec d = (2.1 m/s) (3.0s) + \frac 1 2 (-9.81 m/s^2 [down]) (3)^2
    \\ = 6.3 - 44.145
    \\ = -37.84 [down]##

    Balcony is 37.8 meters high

    b) ## \vec v_2 = 2.1 + (-9.81 m/s^2 [down]) (3.0s)
    \\ = -27.33 m/s [down]##

    Pot was falling at 27.3 m/s when it hit the ground.


    Or if I'm correct with a) is it that I should just divide 37.8 by 3 to get 12.6?
     
  2. jcsd
  3. Apr 16, 2017 #2

    Doc Al

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    Staff: Mentor

    Your method is perfect.

    That gives the average speed, not the final speed.
     
  4. Apr 16, 2017 #3
    Ah. I see. Thank you!
     
  5. Apr 17, 2017 #4

    scottdave

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    Homework Helper
    Gold Member

    One thing to add, if this is an application where significant figures is important, then take note that answers should be limited to two significant figures.
     
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