Question

A 3.30-kN piano is lifted by three workers at a constant speed to an apartment 28.8 m above the street using a pulley system fastened to the roof of the building. Each worker is able to deliver 197 W of power, and the pulley system is 75.0% efficient (so that 25.0% of the mechanical energy is lost due to friction in the pulley). Neglecting the mass of the pulley, find the time required to lift the piano from the street to the apartment.

Answer 1

mg=3300 N, h=28.8 m, Pₒ=197 W

PE =mgh
E= mgh/0.75
P=E/t = mgh/0.75•t = 3•Pₒ
t= mgh/0.75•3• Pₒ =
=3300•28.8/0.75•3•197 =
= 214 s =3.57 min