## anonymous 4 years ago A boy is practicing tennis by hitting a ball at a wall. He hits the ball at 0.75 m above the ground. The initial speed of the ball is 20.0 m/s at an angle of 32 degrees above the horizontal. How long does it take for the ball to hit the wall if it is 6.7 m away?

1. anonymous

You can use these two equation: $y=y_0 +v_0\sin{\alpha}-\frac12 g t^2$ and $x=v_0 \cos{\alpha}*t$ That's all you need

2. anonymous

Can I use either equation to get the answer or do I have to use both somehow?

3. anonymous

You have to use both, you might like to find t from second equation first, then substitute to first equation.

4. anonymous

Ok, I got an answer for t, but I don't understand why I need to plug in that figure to the first equation since I've already found time.

5. anonymous

Good, of course you don't need to. This problem's just overresource. Sorry for my previous answer, i'm not concentrating back then :)

6. anonymous

Lol.. that's ok. :) Thanks for your help!

7. anonymous

Theheh, welcome.