Question

You and two friends are planning on lifting a 4.50 kN piano at constant speed to your apartment 23.0 m above the street level using a pulley system fastened to the roof of the building. Each of you is able to deliver energy at the rate of 145 W by doing work on the rope of a pulley system that is 75.0% efficient. That is, 25.0% of the energy is transformed to other forms due to friction in the pulley. You wish to block off the sidewalk to protect pedestrians while you raise the piano, but are worried because it is a busy street and you may get in trouble with local authorities if you block the sidewalk too long. For what time interval (in min) will the sidewalk be blocked while the piano is moving upward?

min

Answer 1