# Homework Help: Another pre-cal problem

1. Aug 16, 2008

### Lindeza

1. The problem statement, all variables and given/known data
Two stones are launched at the same time from the top of a building, 850 feet high. The first stone is simply dropped over the edge, while the second stone is thrown horizontally at 45 feet/second.
a) which stone will reach the ground first? Explain your answer.
b) About how far apart will the stones be when they land?

If someone gave me the formulas, I could maybe solve the problem. I looked it up my old physics notes, but the formulas there really don't help me...

2. Relevant equations

3. The attempt at a solution
a) The first stone is traveling with 30 feet/second, i suppose. So the second stone is faster.
(even though it is thrown horizontally and has to travel a longer distance?)
Well, at least its an attempt at a solution...

Last edited: Aug 16, 2008
2. Aug 16, 2008

### tiny-tim

Welcome to PF!

Hi Lindeza! Welcome to PF!

hmm … how to help you without actually giving you the answer … ?

Well … this is physics, not philosophy, so any explanation has to be based on an equation.

(and remember, the second stone is thrown horizontally)

What equations can you think of that govern the vertical position of a projectile?

3. Aug 16, 2008

### HallsofIvy

AI would be very surprised if the textbook that had these problems did not have the formulas in the same chapter!

4. Aug 16, 2008

### chislam

Hopefully this should help you with the first question.

Gravity affects all objects' velocity in the vertical direction equally (disregarding air resistance).

5. Aug 18, 2008

### Lindeza

Thanks for helping me!!!
Isn't the vertical position of the projectile
y=t*v*sin(alpha)+0.5gt²
so here it would be:
y= t*45*sin(alpha)+0.5 (-32)*t²+850
but what is alpha?
and how is this supposed to help me?

6. Aug 18, 2008

### Lindeza

They arrive at the same time, I think, right?
(I did a little experiment :D )
Don't know how to do that with formulas or something...but...well...
since the first stone is dropped, it should arrive at x=0, right? so I Just have to find the x value of the other stone??

7. Aug 18, 2008

### tiny-tim

Hi Lindeza!

alpha is zero (because the stone is thrown horizontally).

Does that help?

8. Aug 18, 2008

### Lindeza

that really does help!!!!
but it's too late now, I just sent of the homework assignement and just left out this problem (and the others :D) (I am doing this for summer school, over the internet)
But I don't really think it matters that much...I will still try to solve the problem, because of the final test and because I want to know the answer!!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook