Finding mass given force and acceleration

Click For Summary

Homework Help Overview

The discussion revolves around a physics problem involving the calculation of mass given the force exerted on a woman in an ascending lift with uniform acceleration. The subject area is dynamics, specifically focusing on the relationship between force, mass, and acceleration.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationship between force, mass, and acceleration using Newton's second law. Questions arise regarding the inclusion of gravitational force and how to express it when the mass is unknown. There is also discussion about rearranging equations to isolate variables.

Discussion Status

The discussion has progressed with participants offering insights on how to incorporate gravitational force into the calculations. Some guidance has been provided on writing equations in a way that allows for solving for mass, indicating a productive direction in the conversation.

Contextual Notes

Participants note the challenge of the problem, particularly the lack of initial mass information and the need to consider both gravitational and applied forces in the context of the lift's acceleration.

MMCS
Messages
151
Reaction score
0
a lift ascends with a uniform acceleration of 2m/s^2 whilst transporting a woman. Calculate her mass if the force exerted on her from the floor was 945N.

ANS: 80KG

I have tried F = MA

M = F/A = 945/2 = 472.5

Inertia may have been taken into account but is this possible without being given the mass?
 
Physics news on Phys.org
I hate elevator questions; very tricky!
You have the upward force of 945 N on the lady.
But you forgot gravity also has a grip on her.
Include that, and you will get the 80 kg!
 
I hate them too! how do i include gravity in there? It would usually be the product of her mass and 9.81 but I am not given her mass
 
Write it as mg. You'll have two m's in your F = ma equation but it is not a big problem to collect them as like terms in a linear equation. This is an important idea: write it out even if it strikes you as unsolvable - once it appears in front of you in a mathematical form, a whole different thought process in your mind takes over and often the difficulties disappear.
 
945 - mg - ma = 0
g + a x m = 945
9.81 + 2 x m = 945
m = 945/11.81 = 80kg
Thanks!
 

Similar threads

  • · Replies 23 ·
Replies
23
Views
3K
  • · Replies 21 ·
Replies
21
Views
3K
  • · Replies 38 ·
2
Replies
38
Views
5K
  • · Replies 30 ·
2
Replies
30
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 59 ·
2
Replies
59
Views
5K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
16
Views
2K
Replies
16
Views
2K