If a train travelling at 72 km h⁻¹ is brought to rest by applying brakes in a distance of 200 m, then the retardation of the train is

We use the kinematic equation:
v² = u² +2as
Substituting the values:
0 =(20)²+ 2a(200)
0 = 400 + 400a
400a = −400
a =−1 m/s²
The negative sign indicates retardation.
Thus, the retardation = 1 m/s².
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