# Homework Help: Tennis Projectile Motion Question

1. Oct 5, 2009

### Emethyst

1. The problem statement, all variables and given/known data
A tennis ball is served horizontally at a height of 2.4m, 12m from a net that is 0.9m high. a) If it is to clear the net by at least 0.2m, what is its minimum initial velocity? b) If it clears the net by 0.2m, where will it land? Neglect air resistance for both parts.

2. Relevant equations
Kinematic equations, d=vt

3. The attempt at a solution
I solved this question, but i'm not sure if I went about doing it right, especially for part b). For a) I set the initial vertical velocity to zero, found time using the equation d=v0t + (1/2)at2, and then used this value of time in the equation d=vt to find the initial (horizontal) velocity, which I calculated to be 23.3m/s. For part b) I essentially did the same as a), making the initial vertical velocity zero, calculating the time, and then plugging it into d=vt with the horizontal velocity from part a) to solve for the distance from the net. I wondering for part b) if this would be correct, for I think that the ball would have some form of initial vertical velocity because of gravity, yet my answer of 11.0m seems to make sense in the context of tennis. If anyone can show me which way would the correct method here it would be greatly appreciated, thanks in advance.

2. Oct 5, 2009

### rl.bhat

In the second part they have asked the horizontal distance between the serving point to the landing point. So find the time taken by the to fall through 2.4 m. use this time to find the distance.