What is the explanation for the varying weight readings in an elevator going up?

In summary, the elevator in the Empire State Building accelerates upward and downward. The upward acceleration is greater than 9.8 m/s², and the downward acceleration is less than 9.8 m/s².
  • #1
zellster87
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Homework Statement



You've always wondered about the acceleration of the elevators in the 101-story-tall Empire State Building. One day, while visiting New York, you take your bathroom scale into the elevator and stand on it. The scale reads 150 lbs as the door closes. The reading varies between 120 lbs and 170 lbs as the elevator travels 101 floors.

a.)What is the maximium acceleration upward?
b.)What is the maximium magnitude of the acceleration downward?


Homework Equations



f=mg

The Attempt at a Solution



First of all, i don't understand how the reading on the scale can vary under their weight if the elevator is going up. It seems to me that unless the acceleration is negative, their weight should be positive throughout going up. Where is my logic wrong?
 
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  • #2
For a mass m= kg, the elevator must support its weight = mg =Newtons to hold it up at rest. If the acceleration is a=m/s² then a net force=Newtons is required to accelerate the mass. This requires a support force of F=Newtons. Note that the support force is equal to the weight only if the acceleration is zero, and that if the acceleration is negative (downward), the support force is less than the weight. If you enter a downward acceleration greater than 9.8 m/s² you will get a negative support force, showing that you must force it downward to get an acceleration greater than that of free fall.

elev.gif
 

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  • #3
Ah ok, I got it. Thanks dude.
 
  • #4
What did you get as an answer
 
  • #5
Sorry for resurrecting an old thread, but I really need the help.
I used the formula Fnet = N - Fg and still cannot get the correct answer.
I currently have ma = N - mg where m = 77.11kg, N = 756N, and g = 9.8.
So, 77.11a = 756 - 77.11(9.8)

Where did I go wrong?
Thank you for any help!
 

1. How does acceleration in an elevator affect the passengers?

The acceleration in an elevator can cause the passengers to feel a sensation of weightlessness or a feeling of being pushed down into their seats, depending on the direction of acceleration. It can also cause changes in blood pressure and heart rate.

2. What causes acceleration in an elevator?

Acceleration in an elevator is caused by the motor or pulley system that is responsible for moving the elevator up or down. The motor or pulley system creates a force that moves the elevator and its passengers.

3. Is acceleration in an elevator constant?

In most cases, acceleration in an elevator is not constant. It typically starts at 0 when the elevator is stationary and increases or decreases until the desired speed is reached. However, some elevators may have constant acceleration in order to provide a smoother ride.

4. How is acceleration measured in an elevator?

Acceleration in an elevator is typically measured in meters per second squared (m/s²) or feet per second squared (ft/s²). This measurement is taken by calculating the change in velocity over a period of time.

5. Can acceleration in an elevator be dangerous?

In most cases, acceleration in an elevator is not dangerous as elevators are designed to operate safely within a certain range of acceleration. However, if an elevator experiences sudden or extreme changes in acceleration, it can be dangerous for passengers. Elevators also have safety features, such as emergency brakes, to prevent accidents from occurring due to acceleration.

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