Calculating Moments in AS Physics Homework Question

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SUMMARY

The discussion focuses on calculating moments in AS Physics, specifically using the formula Moment = Force x Perpendicular distance from the pivot point. Participants emphasize the importance of defining clockwise and anticlockwise moments and applying a consistent sign convention. A practical example illustrates the calculation, where a 20N force at a 3m distance generates a moment of 60Nm, while opposing forces of 5N and 10N produce moments of -10Nm and -20Nm, respectively, leading to a net moment of 30Nm.

PREREQUISITES
  • Understanding of basic physics concepts, particularly moments and forces.
  • Familiarity with the formula for calculating moments.
  • Ability to visualize forces and distances in a diagrammatic form.
  • Knowledge of sign conventions in physics calculations.
NEXT STEPS
  • Study the principles of static equilibrium in physics.
  • Learn how to draw free-body diagrams for complex systems.
  • Explore the concept of torque and its applications in mechanics.
  • Practice solving various moment calculation problems using different force configurations.
USEFUL FOR

This discussion is beneficial for AS Physics students, educators preparing students for Cambridge exams, and anyone looking to strengthen their understanding of moments and rotational mechanics.

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Homework Statement


Was doing some past papers in preparation for mock Cambridge exams when I ran into this question. Image should be on here I hope...


Homework Equations


Moment=Force x Perpendicular distance from pivot point?


The Attempt at a Solution


Dunno how to start this one, anyone that can point me in the right direction will be much appreciated!
 

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seiei said:

Homework Equations


Moment=Force x Perpendicular distance from pivot point?

Yes, this is all you need

seiei said:

The Attempt at a Solution


Dunno how to start this one, anyone that can point me in the right direction will be much appreciated!

Well firstly start by taking clockwise moments as positive (or negative, it doesn't really matter)

So which forces would cause a clockwise moments and what are these moments equal to? (write them separately and then add them; also remember your convention so these are positive; negative if you chose otherwise )

Similarly, which forces cause anticlockwise moments, write them down with the appropriate sign?


If you are having trouble with finding the distances, draw a vertical line and horizontal line through P, then for each for each force's direction draw a perpendicular line to it until it intersects with your line through P, this will the perpendicular distance. (Say if the force is vertical, you would draw a horizontal line)
 
Last edited:
Using positive moments as clockwise rotation, The 20N force x 3m distance makes 60Nm. Then with the 5N and 10N forces become -10Nm and -20Nm respectively. 60-20-10= 30Nm which was the correct answer. Thanks heaps!
 

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