An electric hoist draws of electrical power and operates at efficiency

PHYSICS · Single correct · AP · Physics 1: Algebra-based · Work Energy and Power · Work Energy and Power

Problem

An electric hoist draws 40 kW40\,\text{kW} of electrical power and operates at 80%80\% efficiency. It lifts a 500 kg500\,\text{kg} load vertically from rest. Half of the useful mechanical power goes into increasing the load’s kinetic energy, while the other half goes into raising it against gravity. What is the speed of the load after 8 s8\,\text{s}? (a) 20 m s−120\,\text{m\,s}^{-1} (b) 18 m s−118\,\text{m\,s}^{-1} (c) 25 m s−125\,\text{m\,s}^{-1} (d) 22.6 m s−122.6\,\text{m\,s}^{-1}

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