18. The police estimate that for good road conditions the frictional force, F, on a skidding vehicle of mass m is
given by F = 0.8mg. A car of mass 450 kg skids to a halt narrowly missing a child. The police measure the skid
marks and find they are 12.0m long.
(i)
Calculate the deceleration of the car when it was skidding to a halt.
The child's mother says the car was travelling well over the speed limit of 50 kmh but the driver of the car
says she was travelling at 48 kmh and the child ran out in front of her.