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NDA 1 2024 GAT, question 132

Topic: Physics

Q132

A block of mass 2 kg2\text{ kg}, moving with the initial speed of 3 m/s3\text{ m/s} comes to rest on a rough horizontal surface after travelling a distance of 3 m3\text{ m}. The magnitude of the frictional force is :

  1. (a) 9 N9\text{ N}
  2. (b) 3 N3\text{ N}Correct answer
  3. (c) 18 N18\text{ N}
  4. (d) 1 N1\text{ N}

Solution.

Answer: (b) 3 N3\text{ N}

  1. Initial kinetic energy is ½mv² = ½ × 2 × 3² = 9 J.
  2. Friction does 9 J of work over 3 m, so its magnitude is 9/3 = 3 N, assuming the stated uniform rough surface.