- #1
mkwok
- 23
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First of all, I know I've posted this already, but I didn't really understand the reply. I tried going back to the thread, but I can't find it anymore.
A 750 kg elevator starts from rest. It moves upward for 3.00 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?
F=ma
P=FV
(a), since it was asking for the "average" power, so I thought I'd take the average velocity for my equation
so Force = ma = 750*(1.75/3)
and P= 750*(1.75/3)*(1.75/2) = 382.81
However, that is the wrong answer
so I tried it again.. may be I used the wrong numbers? This time I did the following:
Force = ma = 750*(9.8)
and P= 750*(9.8)*(1.75/2) = 6431.25
However, this is still wrong
what am I missing?
(b) I think I am stuck on this part because I don't fully understand part a... but I was actually thinking that may be the power of done by the elevator at cruising speed would just be
P=Fv=mgv = 750*9.8*1.75 = 12862.5
this is definitely wrong because I typed it into my online hw, and it told me its wrong
Homework Statement
A 750 kg elevator starts from rest. It moves upward for 3.00 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?
Homework Equations
F=ma
P=FV
The Attempt at a Solution
(a), since it was asking for the "average" power, so I thought I'd take the average velocity for my equation
so Force = ma = 750*(1.75/3)
and P= 750*(1.75/3)*(1.75/2) = 382.81
However, that is the wrong answer
so I tried it again.. may be I used the wrong numbers? This time I did the following:
Force = ma = 750*(9.8)
and P= 750*(9.8)*(1.75/2) = 6431.25
However, this is still wrong
what am I missing?
(b) I think I am stuck on this part because I don't fully understand part a... but I was actually thinking that may be the power of done by the elevator at cruising speed would just be
P=Fv=mgv = 750*9.8*1.75 = 12862.5
this is definitely wrong because I typed it into my online hw, and it told me its wrong