Kinematics - How high is the balcony

[Evangeline101]

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/s² [down]. Determine how high Marian's balcony is and how fast the flowerpot was moving just before it smashed to the ground.

2. Homework Equations
d= v₁ Δt+ ½ a Δt²
v₂²= v₁² + 2 aΔd

The Attempt at a Solution

Given:

V₁ = 2.1 m/s (up)

a = 9.81 m/s² (down)

t= 3.0 s

Determine how high Marians balcony is:

Δd= v₁ Δ t+ ½ a Δt²

d= (2.1 m/s) (3.0s) - ½ (9.81 m/s²) (3.0s)²

= -37.8 m
Δd = 38 m
Marian’s balcony is 38 m high.


Calculate how fast the flowerpot was moving before it smashed to the ground:

v₂² = v₁² + 2 aΔd


v₂² = (2.1 m/s)² + 2 (9.81 m/s²) (38 m)


v₂² = √750


v₂²= 27 m/s (down)


The flowerpot was traveling 27 m/s (down) before it smashed to the ground.

Is this correct?

 

[gneill]

Looks good.

You could also have determined the final velocity more directly via a formula for velocity given initial velocity, acceleration, and time.

 

[Evangeline101]

Ok thanks for the help :)