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NDA 2017 GAT · General Knowledge · Motion, Forces and Gravitation · hard

A car moving at 20 m/s is braked with a uniform retardation of 5 m/s^2. The distance travelled by it during the last second before it stops is

Single correct option

A car moving at 20 m/s is braked with a uniform retardation of 5 m/s^2. The distance travelled by it during the last second before it stops is
  1. A. 5 m
  2. B. 2.5 m
  3. C. 10 m
  4. D. 7.5 m
Show answer and solution

Answer: (B) 2.5 m

Reverse the motion: a body starting from rest and accelerating at 5 m/s^2 covers (1/2)(5)(1)^2 = 2.5 m in its first second. By symmetry this equals the distance covered in the final second before stopping. Choosing 5 m wrongly uses speed at that moment times one second. The total stopping time is 4 s and distance 40 m.
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Original question written in the NDA 2017 GAT pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake