A 2200-kg sport utility vehicle traveling at 84 km/h can be stopped in 0.21 s if

Question

A 2200-kg sport utility vehicle traveling at 84 km/h can be stopped in 0.21 s if it hits a concrete wall. Assume a 60 kgperson was in the car that hit this wall. The velocity of theperson equals that of the car both before and after the crash, andthe velocity changes in 0.21 s. (a)What is the average force exerted on the person?
1 N (in a directionopposite to the initial motion)

(b) Some people think that they can stop themselves rushing forwardby putting their hands on the dashboard. Find the mass of theobject that has a weight equal to the force you justcalculated.
2 kg

Explanation / Answer

              (a)   Given that the mass of the diver is m = 60 kg            The initial velocity of the diver (car) is U = 84 km/h = (84*5/18 )m/s = 23.33 m/s            The final velocity of the diver is V = 0 m/s            time taken to stop is t = 0.21s ------------------------------------------------------                 From the equation of motion                      a = ( V - U) /t                      a = ( 0 - U ) / t                                                             The net force on the diver is F = ma                                                             = m ( - U ) / t                                                              = ---------- N              If the force is equal to the weight of the body then                                            F = mg                                            m = F / g                                                 =------------ kg               The initial velocity of the diver (car) is U = 84 km/h = (84*5/18 )m/s = 23.33 m/s            The final velocity of the diver is V = 0 m/s            time taken to stop is t = 0.21s ------------------------------------------------------                 From the equation of motion                      a = ( V - U) /t                      a = ( 0 - U ) / t                                                             The net force on the diver is F = ma                                                             = m ( - U ) / t                                                              = ---------- N              If the force is equal to the weight of the body then                                            F = mg                                            m = F / g                                                 =------------ kg   

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