Q6 - A crane lifts a mass

Last updated at September 16, 2026 by

  • 📋 Revise, Reflect, Refine, Q6 (Page 137)
    A crane lifts a mass m to the 10th floor of a building in a certain time. It then raises the same mass to the 20th floor of the same building in double the time. How much more energy and power are required? Assume that the height of all floors is equal.
    GIF Watch: why does the pendulum eventually stop in real life Animation for "Why does the pendulum eventually stop in real life". A short looping GIF, three or four beats, drawn in the flat classroom style of the chapter. Beat 1 — In real life, the pendulum slows down and eventually stops. Beat 2 — This is because of energy loss due to friction at the support and air resistance. Beat 3 — The mechanical energy slowly converts into heat and sound. Label every arrow and quantity, name the direction each force or motion acts in, and hold the last frame for a moment before the loop starts again.
    View answer Hide answer
    Answer
    • Energy
      • Energy = mgh. Height of 20th floor = 2 × height of 10th floor.
      • So energy required is 2 times .
    • Power
      • Power = Work / time
      • Work became 2 times, and time also became 2 times.
      • Power = 2W / 2t = W / t — same as before!
      • So the power required is the same (no more power needed).
Remove Ads
Teachoo · Class 9 Explore Class 9
CA Maninder Singh's photo - Co-founder, Teachoo

Made by

CA Maninder Singh

CA Maninder Singh is a Chartered Accountant with 16+ years of practical experience and 20+ years of teaching experience. At Teachoo, he simplifies Accounts, Tax and GST with step-by-step examples so students can apply concepts confidently in exams and real life.

For an uninterrupted learning experience, students can use Teachoo Black to remove ads and focus better.