# Homework Help: Need help finding what formula to use?

1. Sep 8, 2009

### maegenr8

1. The problem statement, all variables and given/known data
A tennis player hits a ball at ground level, giving it an initial velocity of 26 m/s^2 at 54 degrees above the horizontal. How high above the ground does the ball go?

2. Relevant equations
?

3. The attempt at a solution
I found out the horizontal velocity, which is 15.3 and the vertical velocity which is 21.0

2. Sep 8, 2009

### Jebus_Chris

In projectile motion the highest point occurs right in the middle when the vertical speed is zero.

3. Sep 8, 2009

### maegenr8

Yeah, I understand that. What formula would I use to actually find the height though?

4. Sep 8, 2009

### Jebus_Chris

$$v^2=v_o^2+2a\Delta y$$

5. Sep 8, 2009

### maegenr8

So if at the highest point there is a vertical speed of zero, would I put zero in for v^2? 26 for initial velocity and -9.8 for acceleration?

6. Sep 8, 2009

Yes.

7. Sep 8, 2009

### maegenr8

the answer is 22.6, but when i do that I get 34.49

8. Sep 8, 2009

### maegenr8

ohh... I think I needed to put in the vertical velocity which was 21.0 instead. Then that formula works.