Woman standing on a scale in an elevator accelerating downward

In summary, the conversation is discussing how to calculate the force of gravity acting on a person using Newton's Second Law. The participants are discussing different methods of calculation, including using a free body diagram. The conversation also highlights the importance of understanding and using free body diagrams in physics problems.
  • #1
IceCherryPop
4
0
Homework Statement
A 65 kg women is standing on a bathroom scale while an elevator is accelerating downwards at 2.5 m/s^s.
Relevant Equations
My teacher had told us that when FG>N to add and when FG>N to subtract.
For A, I had multiplied 65 and 9.8 since that’s the force of gravity.
For B, I again multiplied 65 and 2.5 (that’s what the scale says it reads.
*I believe you multiply them for c and d, but I’m not positive for it.
C- I think you multiply then subtract
D- I think you multiply and I’m not sure where to go from there.
 

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  • #2
Add what to what? Far better to use Newton’s 2nd law, sum of all forces acting on person equals mass times acceleration. Note that gravity acts down on her, and the scale normal force acts up on her (normal forces are pushing forces acting toward the person). Acceleration is always in the direction of the net (sum of forces) force.
 
  • #3
PhanthomJay said:
Add what to what? Far better to use Newton’s 2nd law, sum of all forces acting on person equals mass times acceleration. Note that gravity acts down on her, and the scale normal force acts up on her (normal forces are pushing forces acting toward the person). Acceleration is always in the direction of the net (sum of forces) force.
So you would just add all the forces needed then multiply her mass?
 
  • #4
Fnet = ma, where Fnet consists of the weight force acting down and the normal force acting up, m is given, and a is given, downward, part A . Since a is downward, the net force must be downward.
 
  • #5
Let's see your free body diagram. That will help you resolve this. (Did you think you had advanced to the point where you no longer need to draw free body diagrams?)
 
  • #6
Chestermiller said:
Let's see your free body diagram. That will help you resolve this. (Did you think you had advanced to the point where you no longer need to draw free body diagrams?)
My teacher never really taught how to draw one but I asked a friend and they showed me how. For B since both of the forces and going downward I just subtracted it then multiplied to find the force.
 
  • #7
IceCherryPop said:
My teacher never really taught how to draw one but I asked a friend and they showed me how. For B since both of the forces and going downward I just subtracted it then multiplied to find the force.
Assuming gravity is one downward force, what is the other?

What answer did you get?
 
  • #8
PeroK said:
Assuming gravity is one downward force, what is the other?

What answer did you get?
For B, I got 107.25. One of the forces I put was the tension force.
 
  • #9
IceCherryPop said:
For B, I got 107.25. One of the forces I put was the tension force.
What tension force? Assuming your answer is in Newtons, then that cannot be correct.
 
  • #10
IceCherryPop said:
For B, I got 107.25. One of the forces I put was the tension force.
The tension force from the glue on the woman's shoes where they touch the scale?

In a free body diagram, one picks a specific body and identifies all of the forces on that body. Which body did you pick? What tension force on that body are you considering?
 
  • #11
There is no excuse for your teacher not teaching you about free body diagrams. He/she should be ashamed. You will never be able to do physics without this. The proof of this is that you are struggling even with this simplest of problems. Please draw a diagram showing the woman’s body, and draw vector arrows to indicate the forces acting on her body. Label these arrows to indicate the magnitude of the forces. Show us what you get for this free body diagram.
 
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Related to Woman standing on a scale in an elevator accelerating downward

1. How does the weight of a woman change when standing on a scale in an elevator accelerating downward?

When standing on a scale in an elevator accelerating downward, the woman's weight will increase. This is because the scale measures the force that the woman exerts on it, which includes both her weight and the additional force from the elevator's acceleration.

2. Is the woman's weight different if the elevator is accelerating downward versus moving at a constant velocity?

Yes, the woman's weight will be different in these two scenarios. When the elevator is moving at a constant velocity, the scale will measure the woman's true weight. However, when the elevator is accelerating downward, the scale will measure a higher weight due to the added force from the acceleration.

3. Why does the woman feel heavier when the elevator is accelerating downward?

The woman feels heavier because she is experiencing an additional downward force from the elevator's acceleration. This added force is felt as an increase in weight on the scale.

4. Does the woman's mass change when standing on a scale in an elevator accelerating downward?

No, the woman's mass does not change in this scenario. Mass is a measure of the amount of matter in an object, and it remains constant regardless of the forces acting on the object. The scale measures the force that the woman exerts, which is a combination of her weight and the added force from the elevator's acceleration.

5. How does the scale measure the woman's weight in an accelerating elevator?

The scale measures the woman's weight by calculating the force that she exerts on it. In an accelerating elevator, the scale takes into account the added force from the acceleration to determine the total weight being exerted on it.

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