# Electrical power

1. Oct 16, 2008

### lovechild

1. The problem statement, all variables and given/known data

1.Lets look at the motion of a lift in two situations:a) The lift moves upward with a constant speed of 2m/s.how much eletrical power goes the engine of the llift use if the efficiency of the engine is 90% ?
b) Whats the power at time 1.5s when the lift started upwards from rest at time zero with accceleration 0.75 m/s² ? we assume that there are no counterweghts so the engine has to lift the whole mass of the lift which is 950kg. (PS ineed the reply ASP THANKS for the help)

2. Relevant equations

This is the second question!
question (2)
2.A physics student stands in an elevator on a bathroom scale. when the elevator is at rest the scale gives a reading of 560N. as the elevator starts moving, the scale reads 800N. a) Find the acceleration of the elevator (direction and magnitude). b) what is the acceleration if the scale reads 450N? c) if the scale reads zero, should the student worry? explain.(PS ineed the reply ASP THANKS for the help)

3. The attempt at a solution
solution1

F=W = mg = 950*10= 9500N
F-W=ma msince a = 0 then F=W
Pused = 0.9*Pin
Pused = 9500* 2 = 19000

Pin = 10/9*Pused

soulation2
F =ma
w=mg= 560N
w-f = 800N
mg-ma =800N
ma= mg -800N
= 560-800N
=-240N

Last edited: Oct 16, 2008
2. Oct 16, 2008

### nasu

I understand that in the everyday language you can interchange the words power and force.
However this is not so in physics. Power is not the same thing as Force.
You did calculate the force correctly. Now calculate the power. Look up the definition if you did not do it yet. (It is related to work).