Question

Megan is driving her Mercedes, with a mass of 1000 kg, at a speed of 20ms^-1. Calculate the average net force applied to the car if it is to stop in a distance of 25 m to avoid running over a cat.

Answer 1

Retardation a required to stop the vehicle from 20 m/s to 0 m/s is obtained from

v2 = u2 - 2 a S

where v is final speed that is zero , u = 20 m/s is initial speed and S = 25 m is distance covered during retrdation till vehicle comes to rest.

a = u2 / ( 2 S ) = ( 20 20 ) / ( 2 25 ) = 8 m/s2

Average net force = mass acceleration = 1000 8 = 8000 N