# Physics - Projectiles

• Nov 3rd 2008, 08:27 PM
ajj86
Physics - Projectiles
Donovan McNabb passes a football – at a velocity of 50 ft/s at an angle of 40 degrees to the horizontal – toward an intended receiver 30 yd straight downfield. The pass is released 5 ft above the ground. Assume that the receiver is stationary, is isolated and that he can catch the ball from the ground (a shoestring catch) up to a height of 7 ft when the ball arrives at his position. Will the pass be completed? If not will it be short or long? If the conditions (launch height, distance to receiver, height for catch) are exactly the same but the quarterback can launch the football at 45 degrees to the horizontal what is the range of speeds he must give the ball at launch so as to make a completion?
• Nov 4th 2008, 02:18 AM
mr fantastic
Quote:

Originally Posted by ajj86
Donovan McNabb passes a football – at a velocity of 50 ft/s at an angle of 40 degrees to the horizontal – toward an intended receiver 30 yd straight downfield. The pass is released 5 ft above the ground. Assume that the receiver is stationary, is isolated and that he can catch the ball from the ground (a shoestring catch) up to a height of 7 ft when the ball arrives at his position. Will the pass be completed? If not will it be short or long? If the conditions (launch height, distance to receiver, height for catch) are exactly the same but the quarterback can launch the football at 45 degrees to the horizontal what is the range of speeds he must give the ball at launch so as to make a completion?

Here's a start:

Consider the motion of the football in the vertical and horizontal directions:

Horizontal direction:

u = 50 cos(40) m/s
a = 0 m/s^2
x = 30 m
t = ?

Calculate t using an appropriate formula.

Vertical direction:

u = 50 sin(40) m/s
a = -9.8 m/s^2
t = get from above calculation.
y = ?

Calculate y using an appropriate formula.

If y > 2 (yes y > 2, NOT 7. Why ....?) or y < -5 (yes, y < -5 because then the football falls short. Why ....?) the football cannot be caught.