# Homework Help: A Projectile Launcher

1. Sep 17, 2016

### Veronica_Oles

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

A baseball player hits a ball 200.0m home run. The ball travels at angle of 45° with the horizontal just after being hit. Determine the initial speed. Assume the ball lands the same height it was hit.

2. Relevant equations

3. The attempt at a solution

I am not sure how to go about this question. I think range is 200m and I know acceleration is 9.8m/s2[down] but that's about it.

2. Sep 17, 2016

### Staff: Mentor

You must be able to find some relevant equations. Check your course text and notes for equations related to projectile motion.

3. Sep 17, 2016

### Brianna I

Ok, when I was initially taught this I was told to make a chart in both the x and y with what you know and do not know.
The setup would be something like this:
______ X _____ Y
a =
vi =
d =
t =
From there try to solve for maybe t using the y-variables (since you don't have that either) and then plugging in t in an equation that will give you Vix.

4. Sep 17, 2016

### Veronica_Oles

Yes, I did this.

5. Sep 17, 2016

### Staff: Mentor

You need to show what you've done before we can help.

6. Sep 18, 2016

### Veronica_Oles

I have not gotten any of it done because I have no idea which formula to use. All I know is that on my horizontal I have d = 200 m and a = 0. Then for my vertical I have d = 0 and a = 9.8m/s^2(down). I dont have time and all the formulas I was given deal with time which is why I am confused

7. Sep 18, 2016

### haruspex

For motion under constant acceleration, there are five standard variables (usually known as SUVAT, s for displacement, u for initial speed, v for final speed, a for acceleration, t for time). There are correspondingly five equations. Each equation omits one of the five variables. Are you familiar with these?

8. Sep 18, 2016

### Veronica_Oles

Yes I know those.

9. Sep 18, 2016

### haruspex

Since you do not care about time, pick one that does not involve time.

10. Sep 18, 2016

### Veronica_Oles

The only one I see that doesnt involve time is vf^2 = vi^2 + 2ad

11. Sep 18, 2016

### haruspex

Sorry, I wasn't thinking clearly. You do care about time, but you have to start with the horizontal direction. If it is hit with speed v, how long to reach ythat distance?

12. Sep 18, 2016

### Veronica_Oles

T= 200/ViCos 45 ??!

13. Sep 18, 2016

Yes.