# Homework Help: Physics:Projectile Motion

1. Sep 23, 2008

### jarrellboog04

A rifle is aimed horizontally at a target 50m away. The bullet hits the target 2.0cm below the aim point.

A. What was the bullet's fight time?
B. What was the bullet's speed as it left the barrel?

2. Sep 23, 2008

### LowlyPion

Welcome to PF.

How long does it take to drop 2 cm?

3. Sep 23, 2008

### jarrellboog04

It does not give that info

4. Sep 23, 2008

### jarrellboog04

It does not give me the time

5. Sep 23, 2008

### jarrellboog04

I have some equations but i am not sure how to use them

6. Sep 23, 2008

### LowlyPion

Well then figure it out.

You know gravity.
You know the distance.
So ...

7. Sep 23, 2008

### LowlyPion

8. Sep 23, 2008

### jarrellboog04

None of those are the equations i have for the problem i have the answer from the back of the book but that does not help if i do not no how to answer it i tried many differnet ways but still can not find the right way

9. Sep 23, 2008

### LowlyPion

Which of those equations relates gravity, time and position? That is of course if you dropped it from rest, Vo = 0?

10. Sep 23, 2008

### jarrellboog04

i changed the 2cm to .02m to get the same units

11. Sep 23, 2008

### LowlyPion

OK. That you have to do.

So which equation did you try?

12. Sep 23, 2008

### jarrellboog04

I did conversion. I jus figured out the answer to part a i got .064s
i used the equarition
y^f=y^i + (v^y)i delta (t)-1/2g(delta (t)2

13. Sep 23, 2008

### LowlyPion

Right equation. Good result.

Now it traveled 50 m in that time.
How fast you figure it was going to do that?

14. Sep 23, 2008

### jarrellboog04

But now i am trying do part b but cant

15. Sep 23, 2008

### LowlyPion

Now it traveled 50 m in that time.
How fast you figure it was going to do that?

16. Sep 23, 2008

### jarrellboog04

I am going to use this equation and see if i can figure it out
x^f=x^i+(v^x)i delta (t)

17. Sep 23, 2008

### LowlyPion

OK. that works. Xi is 0 of course.

18. Sep 23, 2008

### jarrellboog04

i got Xi to be .02m

19. Sep 23, 2008

### jarrellboog04

i got xi to .o2cm

20. Sep 23, 2008

### LowlyPion

No. When it was aimed it was aimed toward 0. It dropped .02.