Moments and centre of gravityEdexcel A-Level Physics: Flashcards

What these 13 flashcards ask

What is the moment of a force?
What is the unit of moment?
A force F acts at angle θ to a rod of length d from the pivot. What is its moment?
What is the centre of gravity of a body?
Where is the centre of gravity of a uniform beam?
How can you find the centre of gravity of an irregular flat card?
State the principle of moments.
What two conditions are needed for equilibrium?
Why is it helpful to take moments about the point where an unknown force acts?
What is the moment of a force whose line of action passes through the pivot?
A beam on two supports is about to tip about one support. What is the force at the other support?
Why does a hanging card come to rest with its centre of gravity directly below the pin?
When does a tilted object tip over?

Exam questions on Moments and centre of gravity

A mechanic is loosening a stiff wheel nut using a spanner whose handle is 0.35 m long, measured from the centre of the nut to the point where she pushes. She applies a constant force of 120 N at the end of the handle.
Explain why a mechanic can loosen a stiff nut more easily using a longer spanner.2 marks
A student wants to find the centre of gravity of an irregular piece of thick card. He makes a small hole near one edge, hangs the card freely from a pin through the hole, and hangs a plumb line from the same pin.
Explain why the card comes to rest with its centre of gravity vertically below the pin.2 marks
A uniform wooden beam of length 6.0 m and weight 400 N rests horizontally on two supports. Support A is at the left-hand end of the beam and support B is 5.0 m from A, so the right-hand end overhangs B by 1.0 m. A person of weight 900 N stands on the beam 1.5 m from A.
Use the principle of moments to calculate the upward force exerted on the beam by support B.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).