# Homework Help: Can of paint falling down

1. Apr 11, 2007

### ssb

1. The problem statement, all variables and given/known data

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)?

2. Relevant equations

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

Vy = Viy + AyT

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

3. 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 ive 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

2. Apr 11, 2007

### 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.

3. Apr 11, 2007

### 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.

4. Apr 11, 2007

### ssb

and

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?

5. Apr 11, 2007

### 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'.

Last edited: Apr 11, 2007
6. Apr 11, 2007

:!!) :rofl:

Thanks!!!