A boxer stops a punch with his head. To approximate the force ofthe blow, treat

Question

A boxer stops a punch with his head. To approximate the force ofthe blow, treat the opponent's glove, hand, and forearm as aparticle of mass 1.33 kg moving withan initial velocity of 18.5 m/s. (a) Estimate the force exerted on the head ifthe hand moves forward 10.3 cm whiledelivering the blow and then coming to rest.


(b) Estimate the force exerted on the head if the head isdeliberately moved back during the punch so that the hand movesforward 20.6 cm whiledecelerating. (a) Estimate the force exerted on the head ifthe hand moves forward 10.3 cm whiledelivering the blow and then coming to rest.


(b) Estimate the force exerted on the head if the head isdeliberately moved back during the punch so that the hand movesforward 20.6 cm whiledecelerating.

Explanation / Answer

a ) A mass of a particle is m = 1.33kg               moving with a initial velocity v0    = 18.5 m/s , travelled adistance is   s = 10.2 cm = 0.103m                using Kinematic equation v2 -v02 = 2as                                                   ( 0m/s ) 2 - ( 18.5 m/s ) 2 = 2 a(0. 103m )                                                   a = 1661.40 m/s2                                 Force exerted is F = ma                                                             = 1.33 kg * 1661.40 m/s2                                                             = 2210 N b )      using Kinematicequation v2 - v02 =2as    distance s = 20.6 cm =0.206 m                                                     ( 0m/s ) 2 - ( 18.5m/s ) 2 = 2 a(0. 206m )                                             Therefore
    F = m a = 1.33 * 830.70 = 1104.831 N

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