# Theoretical Line

#### Touchme

I have a lab question that states "does your experimental value agree with the theoretical line for projectile motion?" What is a theoretical line and how do I compare these value.

I thought a theoretical line is x=V(sq.root(2h/g)), but im not sure.

Homework Helper
What value did you measure?

#### Touchme

i measured the horizontal distance and and horizontal velocity.

Homework Helper
Touchme said:
i measured the horizontal distance and and horizontal velocity.
So, which is the equation of the displacement in the x-direction? Which is the equation of the horizontal component of velocity? Use these equations to compare your test results with the 'theoretical' values.

#### Touchme

The problem is that the theoretical values are not given. All I have is the equation and a plot of my experimental values. How do I determine the theoretical line that I need to compare my values?

Homework Helper
Well, I guess you have a plot of your experimental values dependent on time, right? So, just plug the 'times' into the 'theoretical' equations and compare the results. I hope I'm not missing something big here.

#### Touchme

It is not a plot dependent on time. The plot is x (distance) vs. horizontal velocity. I plugged the values into the equation above and compared the values. But, is there a way I can draw or determine the theoretical line?

Homework Helper
Touchme said:
It is not a plot dependent on time. The plot is x (distance) vs. horizontal velocity. I plugged the values into the equation above and compared the values. But, is there a way I can draw or determine the theoretical line?
Horizontal velocity is constant and equals vx = v0*cosA, where v0 is the initial velocity and A is its angle. Since it is constant during time, it is represented as a horizontal line in a t-vx coordinate system. Maybe this is what you mean by 'theoretical' line.

#### Touchme

how is it represented in a X vs Vx coordinate system?

Homework Helper
Touchme said:
how is it represented in a X vs Vx coordinate system?
The same. vx is constant for every point x.

#### Touchme

hmm.. i think i got it thanks

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