Q7 - Which factors determine the energy

Last updated at September 16, 2026 by

  • ๐Ÿ“‹ Revise, Reflect, Refine, Q7 (Page 137)
    Which factors determine the energy required to raise a flag from the ground to the top of a tall flagpole using a pulley? Does raising the flag slowly or quickly change the amount of work done? If the speed at which the flag is raised is doubled, how does the power requirement change? Explain your answers.
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    Answer
    • Which factors determine the energy required?
      • Energy required = work done = mgh
      • So it depends on — the mass of the flag (m) and the height of the flagpole (h).
    • Does raising the flag slowly or quickly change the work done?
      • No. Work = mgh — it has no time in it.
      • Slow or fast, the work done is the same .
    • If the speed of raising is doubled, how does the power change?
      • Doubling the speed means the same work is done in half the time .
      • Power = Work / time = W / (t/2) = 2 × (W/t)
      • So the power requirement doubles .
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