Fuel consumed is proportional to kinetic energy gained. The first day total mass is 160 kg, and the second day total mass is 200 kg. The required ratio of fuel used is 160 to 200, which simplifies to 4 is to 5.
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 that the energy transfer to the scooter happens entirely due to fuel, and no other losses occur due to air resistance and friction.
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Since fuel energy converts entirely into kinetic energy, fuel used is proportional to total kinetic energy. On the first day, combined mass is 60 kg plus 100 kg, which equals 160 kg. On the second day, combined mass is 160 kg plus 40 kg, equaling 200 kg. At the same final speed, the ratio of kinetic energies and fuel consumed is 160 to 200, simplifying to 4 is to 5.
For more NCERT Solutions of Class 9 Science Exploration Chapter 7 Work, Energy and Simple Machines Question Answer (2026-27)
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