Here, we have to find out how the minimum distance required to stop a car changes, when the speed of the car is reduced to 2/5th.
We know that,
According to work - energy principle,
Work done in stopping = KE
ie, F.S = ½
mv2 Where,
F - Force
S - displacement
m - mass
v - velocity
If F & ½ m are constants,
S α
v2 When the velocity is reduced (2/5)th of the initial one,
S' α
(v)2 i.e.,
=
S' =
S That is, the minimum distance required to stop the car becomes (4/25)th times of the initial one.