Finding Velocity for 2D Projectile Motion with Given Angle and Distance

[Tearsandrille]

Homework Statement

A football player throws a football at 40 degrees. A stationary player 31.5m downfield is ready to catch the ball. At what velocity does the player have to throw the ball in order to reach the downfield player?

We were told the correct answer is 17.7m/s

Homework Equations

I've been trying to use this equation:
Vy^2 = Voy^2 + 2ad
Voy=Vo*sin(theta)

The Attempt at a Solution

Since, Vy is equal to zero at the peak of the trajectory (15.75m)
So, 0=Voy^2 + 2*9.8m/s^2*15.75m
Solve for Voy and plug it into Voy=Vo*sin(40). Than solve for Vo.

But, I can not seem to get 17.7m/s.

 

[Winzer]

Hello Tearsandrille.

Start off with your kinematic equations:
$$x=x_o + (V Cos(\theta)) t$$
$$y=y_o + (V Sin(\theta)) t-\frac{1}{2} g t^2$$
What do you know? What don't you know?
You should be able to get it from here.