Q8 - A man of mass 60

Last updated at September 16, 2026 by

  • ๐Ÿ“‹ Revise, Reflect, Refine, Q8 (Page 137)
    A man of mass 60 kg rides a scooter of mass 100 kg. He accelerates the scooter to a velocity v. The next day, his son with a mass of 40 kg joins him as a passenger. If the scooter reaches the same speed on both days in the same time interval, what is the ratio of the fuel of the tank used on the two days? (Assume energy transfer is entirely due to fuel, no losses.)
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    Answer
    • Fuel used = energy given to the scooter = kinetic energy gained (starting from rest)
    • Day 1 — mass = 60 + 100 = 160 kg
      • Energy = ½ × 160 × v²
    • Day 2 — mass = 60 + 100 + 40 = 200 kg
      • Energy = ½ × 200 × v²
    • Ratio = 160 : 200
    • Ratio of fuel used = 4 : 5
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