Final Velocity of Falling Paint Can

[ssb]

Homework Statement

A painter is standing on scaffolding that is raised at constant speed. As he travels upward, he accidentally nudges a paint can off the scaffolding and it falls a distance [H1] to the ground. You are watching, and measure with your stopwatch that it takes a time of [T] for the can to reach the ground. Ignore air resistance. What is the speed of the can just before it hits the ground (final velocity)?

Homework Equations

y = Yi + ViyT + 1/2 (AyT^2)

Vy = Viy + AyT

Vy^2 = Viy^2 + 2A(Y-Yi)

The Attempt at a Solution

Ive done this problem with each of the given equations and none seem to work. I was given sample values for H1 = 15 meters and T = 3.25
The answer is suppose to be 20.5 m/s but I've plugged in these numbers a hundred times and gotten several different answers.
Can someone please tell me what equation to use and how to arrive at 20.5 m/s for final velocity? Thanks

 

[Dick]

You need to use your first equation for y to find Viy. Then use the second equation to find Vy. Keep all of the signs straight.

 

[Päällikkö]

The scaffolding is going up, thus Viy is nonzero. You should be able to figure Viy as you're given T (and H1).

EDIT: I'm too slow.

 

[ssb]

You need to use your first equation for y to find Viy. Then use the second equation to find Vy. Keep all of the signs straight.

and

The scaffolding is going up, thus Viy is nonzero. You should be able to figure Viy as you're given T (and H1).

EDIT: I'm too slow.

Thank you so much for this insight. I am going to try it right now

First equation
-15 = 0 + Viy(3.25) +(1/2)(-9.8)(3.25)^2

Viy = 5881/520

Second equation
(5881/520) + (-9.8)(3.25) = Vy = -20.5

Whohoo! the number is correct but it looks like I messed up somewhere with the signs because it should be positive. Hrm... any ideas?

 

[Dick]

The paint can IS going down when it hits, right? Wouldn't that be a negative velocity in your coordinates? Besides, the question asks for 'speed'.

 

[ssb]

The paint can IS going down when it hits, right? Wouldn't that be a negative velocity in your coordinates? Besides, the question asks for 'speed'.

:!)

Thanks!