1. A car is stopped for a traffic signal. When the light turns green, the car ac

Question

1. A car is stopped for a traffic signal. When the light turns green, the car accelerates, increasing its speed from 0 to 4.90 m/s in 0.788 s. (a) What is the magnitude of the linear impulse experienced by a 72.0-kg passenger in the car during the time the car accelerates? kg · m/s (b) What is the magnitude of the average total force experienced by a 72.0-kg passenger in the car during the time the car accelerates? N 2. A rifle with a weight of 20 N fires a 5.5-g bullet with a speed of 240 m/s. (a) Find the recoil speed of the rifle. m/s (b) If a 725-N man holds the rifle firmly against his shoulder, find the recoil speed of the man and rifle. m/s

Explanation / Answer

1)

a) impulse = change in momentum

impulse = 72*4.9 - 72*0 = 352.8 kg.m/s

b)

acceleration of car = (4.9 - 0)/0.788 = 6.22 m/s^2

total average force = 72*6.22 = 447.84 N

2)

a)

conservation of momentum

let recoil speed of rifle = v

so 0.0055*240 = (20/9.8)*v

v = 0.6468 m/s

b)

conservation of momentum

let recoil speed of rifle + man = v

so 0.0055*240 = ((725+20)/9.8)*v

v = 0.017 m/s

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