7-19.) A vertical average force F applied over a height h is required to acceler

Question

7-19.) A vertical average force F applied over a height h is required to accelerate an elevator of mass m from rest up to a steady speed v. (a) How much work is done on the elevator by the applied force? b) What is the kinetic energy of the elevator at steady speed v? (c) What is the potential energy of the elevator at height h? (d) Use the concepts of work and changes in total energy to write an expression for F (e) Calculate the average force that acts on an 850-kg elevator to accelerate it from rest to a speed of 2.0 m/s over a distance of 2.5 m.

Explanation / Answer

a)

work done = W = F h

b)

KE = (0.5) m v2

c)

PE = mg h

d)

F h = (0.5) m v2 + mgh

F = ((0.5) m v2 + mgh )/h

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