Problem Graphic

A construction worker on the new city hall wonders why the elevator has a counterbalance. Does a counterbalance affect the power needed to operate the elevator?

What is known:

• elevator mass m_e = 1000 kg
• elevator load m_c = 1000 kg
• motor efficiency e = 0.8
• elevator speed v_e = 1 m/s

Assume that the elevator moves with constant velocity and all transient accelerations can be ignored.

Problem Diagram

What power (kilowatts) must the elevator motor produce to lift the elevator with

1. an 800 kg counterweight?
2. no counterweight?

• Power is simply work per time, or
    P = ΔU/Δt
  
  
• For computations, use
    P = F·v