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?

Question

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?

anonymous · Answer

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

anonymous · Answer

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

anonymous · Answer

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

anonymous · Answer

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.

anonymous · Answer

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

anonymous · Answer

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

anonymous · Answer

Theheh, welcome.