A placekicker must kick a football from a point 36.0 m (about 40 yards) from the

Question

A placekicker must kick a football from a point 36.0 m (about 40 yards) from the goal. Half the crowd hopes the ball will clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a speed of 22.4 m/s at an angle of 49.0° to the horizontal.

(a) By how much does the ball clear or fall short of clearing the crossbar? (Enter a negative answer if it falls short.)
(???) m
(b) Does the ball approach the crossbar while still rising or while falling? (pick one)

rising

falling   

Explanation / Answer

given initial velocity V0 = 22.4 m/s

intial angle of projetion = 49 deg

Horizontal distance x = 40 yards =120 feet = 36 m

using the components of vvelocity

H COmp---Vx = V cos = 22.4 cos 49 = 14.69 m/s

V Comp ---Vy = V sin = 22.4 sin 49 = 17 m/s

The horizontal displacement is: X = Vxt

t = x / Vx = 36/14.69

t = 2.45 secs

also now use h = Vy t - (1/2) g t2

h = (17*2.45) - (0.5* 9.8*2.45*2.45)

h = 12.23 m

as height ios 3.05 m, d the ball travels , therefore, the ball doe clear the bar

ball rises

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