A 2200-kg sport utility vehicle traveling at 80 km/h can be stopped in 0.20 s if

Question

A 2200-kg sport utility vehicle traveling at 80 km/h can be stopped in 0.20 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 0.20 s. (a) What is the average force exerted on theperson?
N (in a direction opposite to the initialmotion)

(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.
kg (a) What is the average force exerted on theperson?
N (in a direction opposite to the initialmotion)

(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.
kg

Explanation / Answer

             Given that the mass of the mass of vehicle is  M =2200 kg              The initial velocity is U = 80 km/h = ( 80*5/18 )m/s = 22.22m/s               Time taken to stop is t = 0.20s               mass of the person is m = 60 kg               The final velocity of the person and the car is V = 0 m/s          ---------------------------------------------------                    The average force exerted on the person is F =m(V-U)/t                                                                                    = m(0-U)/t                                                                                     =-mU/t                                                                                     =- (60kg*22.22m/s)/0.20s                                                                                    =-6666.66 N         if weight equal tothe force exerted on the person then                                                mg = F                                                  m = F /g                                                       =6666.66 N / (9.8m/s2 )                                                                                  =---------- kg       

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