The front 1.20 m of a 1300 kg car isdesigned as a \"crumple zone\" that collapse

Question

The front 1.20 m of a 1300 kg car isdesigned as a "crumple zone" that collapses to absorb the shock ofa collision. (a) If a car traveling 21.0 m/s stops uniformly in 1.20 m, how long does thecollision last?
1 s

(b) What is the magnitude of the average force on the car?
2 N

(c) What is the acceleration of the car? Express the accelerationas a multiple of the acceleration of gravity.
3g (a) If a car traveling 21.0 m/s stops uniformly in 1.20 m, how long does thecollision last?
1 s

(b) What is the magnitude of the average force on the car?
2 N

(c) What is the acceleration of the car? Express the accelerationas a multiple of the acceleration of gravity.
3g

Explanation / Answer

mass m = 1300 kg initial speed u = 21 m / s distance S = 1. 2 m final velocity v = 0 from the relation v ^ 2- u ^ 2=2aS accleration a = [ v ^ 2- u^2 ] / 2S                     = -183.75 m / s ^ 2 (a). required time t= ( v - u ) / a                             = 0.1142 s (b). average force F = ma                                = 148.57 N (c). Accleration of the car a= -183.75 m / s ^ 2                                         = ( -183.75 / 9.8 ) * g                                         = 18.75 g

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