# Finding the initial velocity of a projectile so that it hits a moving object

1. Oct 6, 2009

### bermy_son92

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

Object is 92m away from the projectile's launch position and is moving towards the launch position at 6m/s.
The projectile is launched at an angle of 72 degrees towards the moving object.
What must the projectile's velocity be if it is to hit the object moving towards it.
(Both the projectile and object start moving at the same time.)
acceleration = gravity = -9.8m/s

2. Relevant equations
distance=velocity/time
distance=velocity*time+0.5*acceleration*time^2
velocity2 - velocity1 = 2*acceleration*distance
velocity2 = velocity1 * acceleration * time

3. The attempt at a solution
I tried a few attempts however none of my ideas worked

2. Oct 11, 2009

### Phrak

Why were the 5 or so subsequent messages posted here deleted?

3. Oct 12, 2009

### BlueFalcon

I uh... don't know. I'm new here. Don't know who could do that.

4. Oct 15, 2009

### Phrak

I consider glitches, means, motive, and opportunity.

5. Oct 15, 2009

### ideasrule

Until we get the posts back...

Note that your last two equations are wrong. The second-last one should be v2^2-v1^2=2ad, not v2-v1=2ad. The last one should be v2=v1+at, not v2=v1*a*t.

To solve this problem, write separate equations for the projectile's horizontal and vertical movements. In the y direction, the projectile leaves at speed=vsin72 and returns to its original height upon hitting the target. Suppose this takes time t. In the x direction, the projectile's relative speed to the target must be enough to cover 92 m in time t. Can you now write out two equations for the projectile's motion?