# Homework Help: Finding the initial speed

1. Oct 4, 2011

### Ki-nana18

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

A baseball player throws a ball a distance of 250 ft. If the ball is released at an angle of 45°with the horizontal, find its initial speed.

2. Relevant equations

3. The attempt at a solution
I don't know where to begin. All i know is that speed is the norm of velocity. Help?

2. Oct 4, 2011

### SammyS

Staff Emeritus
Suppose the initial speed is v0. What are the vertical & horizontal components of the velocity.

3. Oct 4, 2011

### Ki-nana18

x=(v0cos 45°)t
y=(v0sin 45°)t

4. Oct 4, 2011

### minifigmaster

close. You forgot that the y equation has acceleration due to gravity, so that's $\frac{-9.8}{2}$$t^{2}$.

And is that how I'm supposed to do math equations here? Cuz im relatively new (I signed up earlier, I just never used it till now).

5. Oct 4, 2011

### Ki-nana18

Yeah, that's how you do it. And thank you. I should use (32/2)t2 since the unit is feet. Correct?

6. Oct 4, 2011

### minifigmaster

oh yeah, sorry but that, but glad I could help.

7. Oct 4, 2011

### Ki-nana18

So what do i do next? Differentiate?

8. Oct 4, 2011

### minifigmaster

oh i thought you got it. Sorry. You know that x displacement is 250 ft, and y displacement is 0. If you plug that in, you'll find you have a system of two equations with two variables--initial velocity and time. I'm sure you can solve from there.

9. Oct 4, 2011

### Ki-nana18

Thank you so much!