Finding the Distance of a Balanced Seesaw: A Question in Moments

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Homework Help Overview

The problem involves a seesaw with a child and her father, focusing on the concept of moments and balance. The child is positioned at a known distance from the pivot, and the question seeks to determine the father's distance from the pivot based on their weights and the principle of moments.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between mass and weight, questioning the original poster's calculations and assumptions regarding units. There is an exploration of how to compute weight from mass and the implications for solving the problem.

Discussion Status

The discussion is ongoing, with participants providing guidance on understanding weight and its calculation. There is recognition of arithmetic errors in the original attempt, and some participants are clarifying fundamental concepts related to gravitational forces.

Contextual Notes

Participants note the importance of correctly distinguishing between mass and weight, as well as the need for clarity in the application of the moments principle. There is an indication that the original poster may need to revisit foundational concepts in physics.

Robm50
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Homework Statement


"A child and her father are playing on a seesaw. They are exactly balanced when the girl (mass 46 kg) sits at the end of the seesaw, 2.75m from the pivot. If her father weighs 824 N, how far is he from the pivot?"

Homework Equations


(sum of) clockwise moment(s) = (sum of) anticlockwise moment(s)
moment (Nm) = force (N) * perpendicular distance from pivot to line of action of the force (m)

The Attempt at a Solution


girl is mass 46kg (kilograms) whilst her father has weight 824 N (Newtons)?!
46 x 2.75 = y x 824
126.5 = 6.51 * 824
y = 6.51?
= 6.51 metres from pivot?

Please show how you got your answer =]

Thanks,
Robm50
 
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Robm50 said:
126.5 = 6.51 * 824
6.51 * 824 is definitely larger than 126.5 - you have made an arithmetic error.

Edit: Also, the girl has mass 46 kg - not weight 46 N, which is what you seem to be assuming.
 
Orodruin said:
6.51 * 824 is definitely larger than 126.5 - you have made an arithmetic error.

Edit: Also, the girl has mass 46 kg - not weight 46 N, which is what you seem to be assuming.

How would I go about solving this problem, then?
 
What is the weight corresponding to a mass of 46 kg?
 
Orodruin said:
What is the weight corresponding to a mass of 46 kg?

That's exactly my problem; I have no idea how to find such a weight.
 
So, what is weight? If you do not know this you need to go back to your course literature and restudy gravitational forces.
 
Orodruin said:
So, what is weight? If you do not know this you need to go back to your course literature and restudy gravitational forces.

Weight is the result of the gravitational attraction pulling an object's mass particles towards the Earth

Is that correct?
 
Weight is the force with which gravitation pulls an object towards the ground. So how do you compute this force based on the mass of an object?
 
Orodruin said:
Weight is the force with which gravitation pulls an object towards the ground. So how do you compute this force based on the mass of an object?

Would it be as simple as by using the formula:

"Weight = Mass * Gravitational Field Strength"?
 
  • #10
Yes. This will give you the weight of an object.
 
  • #11
Orodruin said:
Yes. This will give you the weight of an object.

Thankyou for your help, Sir.
 

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