# Projectile motion figuring out the variables

1. Oct 4, 2009

### Kaxa2000

I'm working on a problem that gives me the initial velocity and angle at which the ball is thrown and that it happens on the moon, but that's it. So I only have 2 knowns in the x and y direction. I'm supposed to find how far and how high the ball is thrown before striking the ground. Am I able to set the final velocities equal to zero so I can have 3 of 5 variables? The examples I've looked at haven't done that so I'm confused. Is it possible to solve this?

2. Oct 4, 2009

### Delphi51

You've got all you need. The speed, angle and gravity determine the whole flight. Go ahead and write your horizontal and vertical equations and show them here if you would like more help.

3. Oct 4, 2009

### Kaxa2000

ok

so

x-component
dx = ?
vx0 = 44.69cos60
vf =
a = 0
t =

y-component
dy = ?
vy0 = 44.69sin60
vf =
a = -g = -1.62m/s^2(on the moon)
t =

4. Oct 4, 2009

### Delphi51

y-direction
V = Vi + at AND d = Vi*t + .5*a*t^2
V = 44.69*sin(60) - 1.62*t AND y = 44.69*sin(60)*t - .81*t^2

I guess the next step is to get the time of flight, or half of it. There are several ways to do this. Some recall the vertical velocity at half time, others like to use the known velocity at the full time of flight. Or you could use the fact that y = 0 at the end of the flight.

5. Oct 5, 2009

### Kaxa2000

So I would set vf for the y component equal to 0 m/s since at it's highest point the velocity is zero?? Then solve the y component for the displacement to get the distance it is at when it reaches its highest point? Then I could also solve for the time and then multiply it by 2 since at the highest point it's only halfway between the horizontal displacement and then solve for the horizontal displacement.

I need to find the highest point and how far it would travel before striking the ground.

Let me know if this is right..thanks for any help

6. Oct 5, 2009

### Delphi51

All right! You've got it all planned.

7. Oct 5, 2009

### Kaxa2000

Okay...thanks!