# Homework Help: Ball rise trajectory

1. Oct 28, 2004

### UrbanXrisis

A tennis player standing 12.6 m from the net hits the ball at 3 degrees above the hoizontal. To clear the net, the ball must rise at lease 0.33m. If the ball just clears the net at the apex of its trajectory, how fast was the ball moving when it left the racket?

would it just be sqrt(12.6^2+0.33^2) ?

2. Oct 28, 2004

### Leong

no. find an equation relating the horizontal motion of the ball, to reach the net. find another equation relating the vertical motion of the ball to clear the net. solve the equations for v.

3. Oct 28, 2004

### UrbanXrisis

they do not specify time so I could have 12.6m/s ins the x direction and .33m/s in the y direction

hence:
v=sqrt(12.6^2+0.33^2)

4. Oct 28, 2004

### Leong

Origin : the player's position.
Horizontal motion :
s=ut
12.6=(vcos3)*t
Vertical motion :
$$0.33=t*vsin3-\frac{g}{2}t^2$$
Solve the equations for v.