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## Homework Statement

A quarterback throws the football to a stationary receiver who is 31.5m down the field. If the football is thrown at an initial angle of 40.0 degrees to the ground, at what initial speed must the quarterback throw the ball for it to reach the receiver, if the ball is caught at the same level it was thrown?

## Homework Equations

R = (Vo

^{2}*sin(2*theta))/g

## The Attempt at a Solution

The issue I am having is that if gravity is negative I don't get a real number, but I can not understand or explain why gravity would be positive.