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NECO 2002 Physics · Question 32

A body of mass 4 kg is accelerated from rest by a steady force of 9N. What is its speed when it has travelled a distance of 8m?

Options

  1. A.6 ms−1ms^{-1}
  2. B.18 ms−1ms^{-1}
  3. C.32 ms−1ms^{-1}
  4. D.36 ms−1ms^{-1}
  5. E.48 ms−1ms^{-1}

Answer: A. 6 ms−1ms^{-1}

Explanation written with AI and checked against the answer key

Analyze the question: A 4 kg mass starts from rest and is pushed by a constant 9 N force over 8 m. We need its final speed. Concept: The work done by the force becomes kinetic energy (the work-energy theorem). You can also use Newton's second law together with the equations of motion. Solution (Method 1: Work-Energy) Work done = F × d = 9 × 8 = 72 J Kinetic energy gained = ½mv² ½ × 4 × v² = 72 2v² = 72 v² = 36 v = 6 m/s Check (Method 2: Equations of motion) a = F/m = 9/4 = 2.25 m/s² v² = u² + 2as = 0 + 2(2.25)(8) = 36 v = 6 m/s Both methods agree. Answer: The speed is 6 m/s, which is option A. Tip: When a question gives force and distance but not time, go for work-energy (Fd = ½mv²). It skips the intermediate steps. Also, if you see v² = 36, remember to take the square root. Option D (36) is the trap for students who forget this.

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