Afootball kicker is attempting a field goal from 44 m from the goal post. the ball is kicked and just clears the crossbar 2.9 s later. if the angle of the kick was 45°, what was the initial speed of the ball? a. 39 m/s b. 19.7 m/s c. 2.2 m/s d. 21.6 m/s

D. 21.6 m/s

Explanation:

This problem is a projectile motion problem, where we know that the ball reaches a horizontal distance of x=44 m in a time of t=2.9 s. We also know that the ball was kicked with an angle of .

We are only interested in the horizontal motion of the ball, which is a uniform motion with constant speed , where is the initial speed of the ball. The horizontal velocity is simply equal to the ratio between the horizontal distance and the time:

Re-arranging the equation, we find

So, the best answer is

D. 21.6 m/s

acceleration = (change in speed) / (time for the change)

change in speed = (20-120)= -100 m/s.

1.5 min = 90 sec

acceleration = -100/90 = -1.11 m/s^2.

we don't care about the 150kg or the 2,500 meters. they don't make any difference.

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