| | | # Elevator Power.
Asked Feb 20, 2007, 08:18 AM
—
** 7 Answers** | A 550 kg elevator starts from rest. It moves upward for 5.00 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?
W
(b) How does this power compare with the motor power when the elevator moves at its cruising speed?
Pcruising = W
The formula for average power is avg. power = work/change in time
However, I am not sure how to find the work in the problem since no force or angle is given... Is gravity the only force doing work and is the angle 90? |
7 Answers
| Uber Member | |
Feb 20, 2007, 09:35 AM
| | The angle is 0 (you don't need to worry about it, because it's a 1d problem), the motor is doing work against the force of gravity. | | | New Member | |
Feb 20, 2007, 02:12 PM
| | Ok so the F in the problem is 9.8m/s^2. I would use cos0. However, the change in distance is unknown. Using the formula d=time * speed, I found it to be 8.75m. So, now would I use the work formula with the numbers (9.8m/s^2)(8.75m)(cos0). Which equals 85.57J. After I find that I would divide work by time (5secs) to find average power which is 17.15 W... just my thinking? | | | Uber Member | |
Feb 20, 2007, 02:33 PM
| | F = ma :)
your distance is wrong because it's accelerating, you need to use suvat equations | | | New Member | |
Feb 20, 2007, 03:01 PM
| | The force in this problem would be the mass of the elevator time the acceleration which is 1.75m/s correct. So f in the problem would be 962.5N. For distance I mult. The speed times the time. That is the only way I know to find distance. | | | Uber Member | |
Feb 20, 2007, 03:13 PM
| | acceleration is the acceleration of gravity!!
you need to use s = ut + 1/2at^2 to find distance traveled, because it is under constant acceleration.
I have to hit the sack now, but I will carry on tomorrow. | | | New Member | |
Feb 20, 2007, 04:22 PM
| | One more try:
f=mass*acceleration
f=550*9.8=5390N
change in distance=122.5m
cosign of angle 0degrees
w=f*change in d*cosign0
w=5390*122.5*cosign0
?? Correct? | | | Uber Member | |
Feb 20, 2007, 11:31 PM
| | Oh no, your acceleration for s = ut + 1/2 at^2 is 1.75/5 | | Question Tools | Search this Question | | | ##
Check out some similar questions!
Elevator [ 2 Answers ]
What is the force (in Newtons) used if an elevator lifts passengers 30 meters in 24 seconds and the elevator is 15,000 watts?
Car won't start, no click and no power to radio, power window or locks [ 6 Answers ]
After installing a new starter on a 1999 2WD Explorer it will not start. There is no click when trying to start it, its just dead, and the radio, power locks/windows, a/c, and dash light don't work but the interior lights work and so do the headlights. We've had the starter checked to make sure...
Power comes and goes ALL BY ITSELF [ 5 Answers ]
To whomever can help me.
I replaced my panel box about 5 years ago and head it inspected by the county inspector. I passed the inspection and all has worked well. The last month or so I have had power problems. The lights and power outlets would flicker like their wasn't enough power getting...
View more questions Search |