Projectile Motion: Calculating Flight Time and Initial Speed

[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?

Please HELP!

 

[LowlyPion]

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?

Please HELP!

Welcome to PF.

How long does it take to drop 2 cm?

 

[jarrellboog04]

It does not give that info

 

[jarrellboog04]

It does not give me the time

 

[jarrellboog04]

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

 

[LowlyPion]

It does not give me the time

Well then figure it out.

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

 

[LowlyPion]

Here are some equations:
https://www.physicsforums.com/showpost.php?p=905663&postcount=2

 

[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

 

[LowlyPion]

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

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

 

[jarrellboog04]

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

 

[LowlyPion]

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

OK. That you have to do.

So which equation did you try?

 

[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

 

[LowlyPion]

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

Right equation. Good result.

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

 

[jarrellboog04]

But now i am trying do part b but cant

 

[LowlyPion]

But now i am trying do part b but cant

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

 

[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)

 

[LowlyPion]

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

OK. that works. Xi is 0 of course.

 

[jarrellboog04]

i got Xi to be .02m

 

[jarrellboog04]

i got xi to .o2cm

 

[LowlyPion]

i got Xi to be .02m

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

 

[jarrellboog04]

u still can not figure it out

 

[LowlyPion]

u still can not figure it out

Which component are you talking about?

The time times x-Velocity is 50m.

x-Velocity is 50m/.064s

This is not rocket science. Oh, wait a minute, it is.

 

[jarrellboog04]

I meant to say i still can not fingure it out

 

[jarrellboog04]

thanks

 

[ak1991]

this is hard