A car moving at 72km/h is brought to rest in 4s by applying brakes. What is the retardation?
Convert speed: 72km/h=72⋅10003600=20m/s. As per NCERT Chapter 3, equations v=u+at, s=ut+½at², v²=u²+2as describe uniformly accelerated motion. Applying correct signs and units gives 20 m/s as the result, so option A is correct.
Ref: NCERT Class 11 Physics > Chapter 3: Motion in a Straight Line > Topic: Equations of Motion and Problem Solving