A car moving at 20 m s⁻¹ is uniformly retarded. During the 5th second after the brakes are applied, it travels 11 m. The car comes to rest after:
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A car moving at 20 m s⁻¹ is uniformly retarded. During the 5th second after the brakes are applied, it travels 11 m. The car comes to rest after:

G1 Physics · Accepted Answer

Displacement in the 5th second is s₅ = u + (a/2)(9). Hence 11 = 20 + 4.5a, so a = −2 m s⁻². Using v = u + at at rest: 0 = 20 − 2t, giving t = 10 s.