# 2D Kinematics - Finding Initial Velocity

1. Aug 23, 2011

### whoopie88

1. The problem statement, all variables and given/known data
The "hang time" of a punt is measured to be 3.50 s. If the ball was kicked at an angle of 69.0° above the horizontal and was caught at the same level from which it was kicked, what was its initial speed? (Neglect air resistance.)

2. Relevant equations
All Kinematics Equations

3. The attempt at a solution
Acceleration (y) = -9.81 m/s^2
Acceleration (x) = 0 m/s^2
Time = 3.5 s
Vi,x = (Vi)cos69
Vi,y = (Vi)sin69

Now I don't think I have enough information to solve the problem, but I know the problem isn't written incorrectly. I don't know where to go with the information I have because I can't solve for anything.

2. Aug 23, 2011

### bp_psy

You know the "hang time" therefore you can deduce the time it takes to reach the highest point. At that point there is something that happens with your Vy. If you use that with Vi,y = (Vi)sin69 and an appropriate kinematic equation you can solve the problem.

3. Aug 23, 2011

### whoopie88

How can I deduce the time it takes to reach the maximum height? Is that just half of the hang time?

4. Aug 23, 2011

### bp_psy

The ball is caught at the same height from which it was kicked and the acceleration is constant. Energy is conserved. Do you see any reason for the way up to take more then the way down?

5. Aug 23, 2011

### whoopie88

Oh, no I don't. Okay, thank you. I found the correct solution. Thank you!