Power of Elevator Motor: 500kg Acceleration & Cruising Speed

[Geminiforce]

Homework Statement

A 500 kg elevator starts from rest. It moves upward for 3.50 s with constant acceleration until it reaches its cruising speed, 1.75 m/s.
(a) What is the average power of the elevator motor during this period?
(b) How does this power compare with the motor power when the elevator moves at its cruising speed?
Pcruising = ?

Homework Equations

F=ma
P=W/deltaT
W=Fdelta(r)cos(theta)

The Attempt at a Solution

This problem, I first found the acceleration using Vf= Vi +at
a= 0.5m/s^2

Next I plugged this into delta x = volt +1/2a(t^2) and found delta x to be 3.0625
Next, I solved for tension using: T-Mg = Ma
T= M(a+g) = 10,578.75 W
Is this correct? If it isn't, can someone explain to me how to approach this problem?

 

[Hootenanny]

Homework Statement

A 500 kg elevator starts from rest. It moves upward for 3.50 s with constant acceleration until it reaches its cruising speed, 1.75 m/s.
(a) What is the average power of the elevator motor during this period?
(b) How does this power compare with the motor power when the elevator moves at its cruising speed?
Pcruising = ?

Homework Equations

F=ma
P=W/deltaT
W=Fdelta(r)cos(theta)

The Attempt at a Solution

This problem, I first found the acceleration using Vf= Vi +at
a= 0.5m/s^2

Next I plugged this into delta x = volt +1/2a(t^2) and found delta x to be 3.0625
Next, I solved for tension using: T-Mg = Ma

Your method looks good up until this point:

T= M(a+g) = 10,578.75 W

Perhaps this is a typo but, tension is a force and not power.

 

[HallsofIvy]

Homework Statement

A 500 kg elevator starts from rest. It moves upward for 3.50 s with constant acceleration until it reaches its cruising speed, 1.75 m/s.
(a) What is the average power of the elevator motor during this period?
(b) How does this power compare with the motor power when the elevator moves at its cruising speed?
Pcruising = ?

Homework Equations

F=ma
P=W/deltaT
W=Fdelta(r)cos(theta)

The Attempt at a Solution

This problem, I first found the acceleration using Vf= Vi +at
a= 0.5m/s^2

Next I plugged this into delta x = volt +1/2a(t^2) and found delta x to be 3.0625

Why? The problem did not ask for distance moved.

Next, I solved for tension using: T-Mg = Ma
T= M(a+g) = 10,578.75 W

No, the units are wrong. kg (m/s² is Newtons, not Watts. This is a force not power. Do you know how to convert from force to power, i.e. from Newtons to Watts?

Is this correct? If it isn't, can someone explain to me how to approach this problem?

 

[Geminiforce]

Why? The problem did not ask for distance moved.


No, the units are wrong. kg (m/s² is Newtons, not Watts. This is a force not power. Do you know how to convert from force to power, i.e. from Newtons to Watts?

You're right i accidently put the force in the wrong units...
I meant to put Power=M(a+g)(v)... However the question asks for the average power and I think the power calculated there is the power at 3 second. Would this power i just calculated be the cruising speed?