Question 33 Bumpers on cars are not of much use in a collision. To see why, calc

Question

Question 33

Bumpers on cars are not of much use in a collision. To see why, calculate the average force a bumper would have to exert if it brought a 1200 kg car (a so-called "compact" model) to a rest in 15 cm when the car had an initial speed of 2 m/s (about 4.5 mph). Bumpers are built with springs which compress to provide a stopping force without (hopefully) denting the metal.

Question 33 options:

1.6 × 104 N

6.5 × 105 N

3.2 × 104 N

1.8 × 104 N

5.4 × 104 N

1.6 × 104 N

6.5 × 105 N

3.2 × 104 N

1.8 × 104 N

5.4 × 104 N

Explanation / Answer

apply the force on bumber F = ma

where m is mass = 1200 kg

and a is accleration = ?

so use the kinematic equation v^2 = 2aS

where S is distance

v is speed = 4.5 mph

1mph = 0.4470 m/s

so

V = 4.5 * 0.4470 = 2.011 m/s

so

a = v^2/2S

a = 2.011* 2.011/(2* 0.15)

a = 13.48 m/s^2

so

net force F = ma = 1200* 13.48

F = 1.61 *10^4 N , optiop 1 it is --------<<<<<<<<<<<Answer

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