Kinematics Question: Falling object

[Catchingupquickly]

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?

 

[Doc Al]

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.

 

[Catchingupquickly]

Ah. I see. Thank you!

 

[scottdave]

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.