The correct option is C 400 m
Assumption: Initial direction of velocity is positive.
Given:
Initial speed, u=40 ms−1
Acceleration, a=−2 ms−2
Acceleration is negative because it is opposite to the direction of initial velocity.
As the train finally stops, final velocity, v=0
Let the distance traveled by train before stopping be s.
Using equation of motion,
v2=u2+2as
Substituting values,
02=402+(2×−2×s)
Solving, we get:
s=+400 m