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

ID: 1666619 • Letter: A

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 1.47 kg moving with aninitial velocity of 18.0 m/s. (a) Estimate the force exerted on the head ifthe hand moves forward 12.0 cm whiledelivering the blow and then coming to rest.
1 N

(b) Estimate the force exerted on the head if the head isdeliberately moved back during the punch so that the hand movesforward 24 cm while decelerating.
2 N (a) Estimate the force exerted on the head ifthe hand moves forward 12.0 cm whiledelivering the blow and then coming to rest.
1 N

(b) Estimate the force exerted on the head if the head isdeliberately moved back during the punch so that the hand movesforward 24 cm while decelerating.
2 N

Explanation / Answer

a ) A mass of a particle is m = 1.47kg               moving with a initial velocity v0    = 18.0 m/s , travelled adistance is   s = 12.0 cm = 0.12 m                using Kinematic equation v2 -v02 = 2as                                                   ( 0m/s ) 2 - ( 18.0m/s ) 2 = 2 a(0. 12 m )                                                   a = 135 m/s2                                 Force exerted is F = ma                                                             = 1.47 kg * 135 m/s2                                                             = 198 N b )      using Kinematicequation v2 - v02 =2as    distance s = 24 cm = 0.24m                                                     ( 0m/s ) 2 - ( 18.0m/s ) 2 = 2 a(0. 24m )                                                     a = 675 m/s2                                                             Force exerted is   F = ma                                                               = 1.47 kg *   675 m/s2                                                                 = 992N                                                                                                                    Force exerted is   F = ma                                                               = 1.47 kg *   675 m/s2                                                                 = 992N