# Apparent weight of a man standing in an elevator

• Tavon
In summary: Yes, since there is no acceleration, there is no Fnet and the normal force would equal the force of gravity acting on the man, which is 785 N. In summary, the apparent weight of the man standing on a scale in a stationary elevator is 785 N. When the elevator is accelerating downwards at a rate of 1.10 m/s^2, the apparent weight decreases to 697 N. On the other hand, when the elevator is accelerating upwards at a rate of 1.10 m/s^2, the apparent weight increases to 873 N. Finally, when the elevator is moving upwards at a constant velocity, the apparent weight remains at 785 N. This is because in the absence of acceleration, the
Tavon

## Homework Statement

An 80.0 kg man is standing on a scale calibrated in Newtons inside an elevator. Determine the apparent weight of the man as shown by the scale as the elevator is
a. stationary. [ans.785 N]
b. accelerating downwards at a rate of 1.10 m/s^2. [ans. 697 N]
c. accelerating upwards at a rate of 1.10 m/s^2. [ans. 873 N]
d. moving upwards at a constant velocity. [ans. 785 N]

## Homework Equations

Fnet= ma

3. The Attempt at a Solution [/B]
For a. I used the equation Fnet=ma and multiplied 80 by 9.81 and got 785 N, but when I tried the same method for b. (80 kg * 1.10 m/s^2) I got 88 N. This is wrong and I can't figure out how to solve it, I now that the apparent weight will decrease since the elevator is going downwards. I feel like the method for solving c. and d. is going to be the same as the method for solving b..

For part a) the acceleration is 0, as the elevator and man are stationary. So, why didn't you calculate the apparent weight as 0?

Nathanael
That's what I thought at first but the answer in my Physics 20 workbook said 785 N and I tried the method mentioned earlier to get the answer but I didn't understand how it worked. I thought it might be 785 N since gravity is 9.81 and it is still acting on the elevator even though it isn't moving.

Tavon said:
That's what I thought at first but the answer in my Physics 20 workbook said 785 N and I tried the method mentioned earlier to get the answer but I didn't understand how it worked. I thought it might be 785 N since gravity is 9.81 and it is still acting on the elevator even though it isn't moving.
Does gravity stop acting when the elevator moves?

I don't think so. It doesn't say so in the question so I guess it still applies force on the elevator.

Tavon said:
I don't think so. It doesn't say so in the question so I guess it still applies force on the elevator.

You may be missing the key concept about forces. If you are standing on the ground, how many forces are acting on you?

2? Normal Force and Fg?

Tavon said:
2? Normal Force and Fg?
Yes. What about in an elevator accelerating downwards?

Force applied as well or Tension since the cables lower it?

Tavon said:
Force applied as well or Tension since the cables lower it?
I meant the man in the elevator. What are the forces on him?

Fg and Normal Force but if the elevator is accelerating down the man's apparent weight will decrease.

Tavon said:
Fg and Normal Force but if the elevator is accelerating down the man's apparent weight will decrease.

Yes. So what can you say about the normal force?

It stays the same.

Wait it increases...?

Tavon said:
Wait it increases...?

Think about the forces on the man. Gravity pushes him down and the normal force pushes him up.

If he is accelerating downward, then ...?

Then normal force has to try harder to push him up, but its magnitude is still lower than the magnitude of gravity.

Tavon said:
Then normal force has to try harder to push him up, but its magnitude is still lower than the magnitude of gravity.

I would say the normal force must be less than gravity. Acceleration is caused by an imbalance in forces.

Anyway, the other important question is what is the reading on the scales in relation to these forces?

As gravity increases apparent weight decreases and as normal force increases apparent weight increases?

Tavon said:
As gravity increases apparent weight decreases and as normal force increases apparent weight increases?

I'm going offline now, so maybe someone else can pick this up.

No. Gravity is constant. It doesn't change.

Ok. Thankyou.

I solved a), b), and c) using the method in the attachment, but I am not sure how to solve d).

Last edited:
Tavon said:
I solved a), b), and c) using the method in the attachment, but I am not sure how to solve d).
If the man is moving upward with a constant velocity, what is his acceleration?

0?

Tavon said:
0?
Right. So if Fnet=ma, what does that tell you about Fnet?

Fnet= ma
Fnet= 80.0 kg x 0
Fnet = 0

Can you see your way from there to the answer to d) ?

## 1. What is the apparent weight of a man standing in an elevator?

The apparent weight of a man standing in an elevator is the weight that he feels while standing in the elevator. This weight can vary depending on the movement of the elevator.

## 2. How does the apparent weight of a man change in an elevator?

The apparent weight of a man changes in an elevator due to the acceleration or deceleration of the elevator. When the elevator is moving up, the man will feel heavier, and when the elevator is moving down, the man will feel lighter.

## 3. What factors affect the apparent weight of a man in an elevator?

The apparent weight of a man in an elevator is affected by the acceleration of the elevator, the gravitational force, and the normal force exerted by the elevator floor on the man's feet.

## 4. How does the apparent weight of a man in an elevator differ from his actual weight?

The apparent weight of a man in an elevator is different from his actual weight because it takes into account the additional forces acting on the man due to the elevator's movement, while the actual weight only considers the force of gravity on the man's body.

## 5. Can the apparent weight of a man in an elevator ever be greater than his actual weight?

Yes, the apparent weight of a man in an elevator can be greater than his actual weight when the elevator is accelerating upwards. This is because the normal force exerted by the elevator floor on the man's feet is greater than the force of gravity, resulting in a greater apparent weight.

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