# Mechanics Projectile Motion Question

1. Sep 20, 2004

### Antagonist

Hi,

I am new here and I am doing A-Level Maths and Physics. I am currently having trouble in A2 maths. I am doing M2 and am doing projectile motion.
This is the question I am having trouble with:

A tennis ball is served horizontally from a height of 2.3m and it strikes the ground at a point 28m away from the server. Find its height when it passes the net 12m from the server.

I have been trying to work it out but the 5 equations of motion do not seem to work as I do not have enough information. All they give me in this questions is distances. What is the velocity(initial and final), time and most importantly the answer to the question. I am not sure if the velocity and time is needed for the answer. This is probably very simple but its stumped me. If anyone could help it would be much appreciated.

Thanks,

--Antagonist

2. Sep 20, 2004

### arildno

Do you know the height of the net?
EDIT:
OK, sorry about that, you don't need it.
Now, the ball is launched horizontally, that is has zero vertical velocity to begin with.
Hence, you may find the time the ball strikes the ground.
Secondly, since you know it has traveled horizontally 28 meters, you may solve for initial velocity.

Last edited: Sep 20, 2004
3. Sep 20, 2004

### Antagonist

I followed your instructions and that led me to the answer. I figured out the time and initial velocity and then found out the time for it to travel 12m using the initial velocity I found out earlier. Then I found out the distance it fell using the time and acceleration due to gravity. Finally I subtracted the distance it fell from the beginning distance and that is the answer. :)