# Homework Help: SeniorPhysics Graded Assignment Help-Horizontal/Vertical Displacement

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1. Oct 8, 2014

### Elle1121

1. The problem statement, all variables and given/known data
A student is rolling a baseball off the roof of their house into their backyard pool.The house is 20 feet tall, and they roll the baseball off the flat roof at speed of 3 m/s towards the pool. How long is the ball in the air and how far away is the distance the pool must be from the house so that the ball hits the water?

I'm just not sure which of the three equations below to use!

2. Relevant equations
Horizontal displacement at a constant velocity: Change in X=v(t)
Vertical displacement due to free fall: 1/2g(t^2)
Vertical velocity due to free fall: V=gt

3. The attempt at a solution

I took a stab at it, and I got two seconds for the time and 20 feet for the distance. I'm pretty sure they're both wrong though. Thanks for the help!

2. Oct 8, 2014

### CWatters

Can you show your working? For example how did you get 2s for the time to fall 12ft (6m) ?

3. Oct 8, 2014

### Staff: Mentor

Hi Elle1121. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

x = ½gt²

This has two variables, and if either is known you can use the equation to calculate the other variable. Is that going to help you here?

It seems that this problem statement mixes feet and meters, or is this your typing mistake?

Last edited by a moderator: May 7, 2017
4. Oct 8, 2014

### Elle1121

The problem mixes feet and meters on purpose; my teacher wants us to get used to converting them. Also, thank you so much for your help!

Last edited by a moderator: May 7, 2017