Physics Help Plz...Energy?

Question

Compared to some original speed, how much work must the brakes of a car supply to stop a car moving four times as fast? How will the stopping distance compare?

Answer 1

Let
W1=Ke1= 0.5 mV1^2
W2=Ke2=0.5 mV2^2

V2=4V1

W2/W1= 0.5 mV2^2/0.5 mV1^2
W2/W1= V2^2/V1^2
W2/W1= (4V1)^2/V1^2
W2/W1= 16

Since Work equal force times distance
W=Fs and F=constant then the distance s will increase
16 times for 4 times increase in speed.