Posted by Elisa on .
A quarterback throws a football toward a receiver with an initial speed of 21 m/s at an angle of 30° above the horizontal. At that instant, the receiver is 12 m from the quarterback. In what direction and with what constant speed should the receiver run in order to catch the football at the level at which it was thrown?
I keep getting 14.58, but it's incorrect.

physics 
drwls,
The distance the ball travels to reach the level it was thrown is
[V^2/(g)] sin (2A) = 39 m
The receiver must run a distance of 3912 = 27 m during the time the ball is in the air above arm level, which is 2 V sin A/g = 2.14 s. The required speed is 39 m/2.14 s = 18.2 m/s. No human can run that fast.