The Blasted Elevator Questions; General Physics- Please help

In summary, the conversation discusses a problem involving finding the magnitude of an elevator's acceleration while a person is standing on a scale. The person's weight and the scale readings are given, and the process for solving the problem is explained. The correct method involves finding the mass and the difference between the person's weight at rest and on the elevator, and then dividing by the mass to find the acceleration. The net force is not equal to the scale reading, but rather the sum of the normal force and the person's weight.
  • #1
dext
2
0
hey everyone,
sheesh, our professor has us do our homework online, and I SWEAR my answer is right, but apparently it isnt. Here is the question:

You leave the doctors office after your annual checkup and recall that you weighed 684N. You then step onto an elevator with a scale. Find the magnitude of the elevator's acceleration if the scale reads 724N.

How do i solve this problem?
Thanks.
 
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  • #2
Essentially, what I did was divide her weight in the drs office by 9.8, then I entered that mass into Newtons 2nd law equation. I divided 724 by mass--- Doesn't that give me the acceleration?
 
  • #3
You're supposed to show your work when asking questions. We're not doing your homework for you.

However, find the mass, m = 684/9.81 = 69.7 kg. Find the difference between your weight at rest and your weight on the accelerating elevator. 724-684 = 40 N. Now, find the acceleration. a = 40/69.7 = 0.574 m/s^2.
 
Last edited:
  • #4
dext said:
Essentially, what I did was divide her weight in the drs office by 9.8, then I entered that mass into Newtons 2nd law equation. I divided 724 by mass--- Doesn't that give me the acceleration?

The net force is not 724N. 724N is the sum of the normal force exerted by the elevator and your weight.
 

1. What causes an elevator to suddenly drop or stop?

There are several possible reasons for an elevator to suddenly drop or stop. These include mechanical failures, such as a broken cable or faulty brakes, power outages, or improper loading of the elevator. In rare cases, extreme weather conditions or earthquakes can also affect the movement of an elevator.

2. How do elevators know which floor to stop at?

Elevators are equipped with sensors and algorithms that detect and calculate the distance traveled and the direction of movement. The elevator control system then determines the appropriate floor to stop at based on the input from these sensors.

3. Why do elevators sometimes feel like they are accelerating or decelerating?

Elevators use a system of pulleys and counterweights to move up and down. When the elevator starts moving, the counterweight helps it accelerate quickly to match the speed of the elevator car. Similarly, when the elevator approaches its destination floor, the counterweight helps to slow it down smoothly.

4. What is the maximum weight an elevator can hold?

The maximum weight an elevator can hold varies depending on the type and capacity of the elevator. As a general rule, standard elevators can hold anywhere from 2,000 to 5,000 pounds. However, it is important to follow the posted weight limit in elevators to ensure safe and efficient operation.

5. How do elevator doors open and close?

Most elevators use a system of sensors and motors to open and close the doors. When the elevator reaches a floor, the sensors detect the presence of the floor and signal the doors to open. Similarly, when the doors are closing, the sensors will detect any obstruction and prevent the doors from closing until it is safe to do so.

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