Kinematics Question: Falling object

  • #1

Homework Statement


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?

Homework 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##

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?
 

Answers and Replies

  • #2
Doc Al
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Your method is perfect.

Or if I'm correct with a) is it that I should just divide 37.8 by 3 to get 12.6?
That gives the average speed, not the final speed.
 
  • #3
Ah. I see. Thank you!
 
  • #4
scottdave
Science Advisor
Homework Helper
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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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