By the Work-Energy Theorem, the work done in stopping the car = change in kinetic energy.
w = F x d = 0.5 mv2 d = 0.5 mv2 / F
W = F x D = 0.5 mV2 D = 0.5 mV2 / F
Since V = 2v D = 0.5 m(2v)2/ F
D = 4 (0.5 mv2/ F) = 4d
Hence, the stopping distance is quadrupled if the speed is doubled.
Answer: 48 m