A 79.0kg wide receiver is running parallel to the sideline with a speed of 9.0 m

Question

A 79.0kg wide receiver is running parallel to the sideline with a speed of 9.0 m/s. A 74.0 kg cornerback tackles (inelastic collision) him at an angle of 60 degree from behind with a speed of 9.3m/s. Is a touchdown scored if the initial contact is made at the 8-yard line 5 yards from the sideline? Include the following information as proof of your answer. What is the velocity of the players immediately after the collision? At what angle relative to the original direction of the wide receiver do they travel after the collision? What percent of the initial kinetic energy is lost in the collision (immediately after the collision)?

Explanation / Answer

2) Using momentum conservation,

[79 x 9 i] + [74 x 9.3 (cos60i + sin60j) ] = (79 +74)Vf

Vf = 6.90i + 3.90 j

a) speed = sqrt ( 6.90^2 + 3.90^2) = 7.93 m/s

angle = tan^-1( 3.90 / 6.90) =29.48 degrees

B) angle = 29.48 degrees

c) initial KE = 79 x 9^2 /2 + 74 x 9.3^2 /2

KEi = 6399.63 J

Final KE = (79 + 74) x 7.93^2 /2 = 4810.69 J

Energy lost = 6993.63 - 4810.69 =2182.94 J

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