MomentsAQA A-Level Maths: Flashcards

What these 13 flashcards ask

Define the moment of a force about a point.
What is the unit of moment?
State the principle of moments.
Two conditions for equilibrium of a rigid body?
Where does the weight of a uniform rod act?
What does a 'light' rod mean?
Moment of a force F at angle \theta to a rod, at distance d along it?
Which point is best for taking moments?
What happens at a support when a rod is about to tilt about the other support?
How do you find the centre of mass of a non-uniform rod?
What does 'model as a particle' mean for a person on a rod?
In the principle of moments, do distances need to be from one point?
Name a modelling assumption for a beam on supports.

Exam questions on Moments

A light plank is balanced horizontally on a smooth pivot. A child of mass $30$ kg sits $1.5$ m from the pivot on one side, and a second child of mass $m$ kg sits $2$ m from the pivot on the other side. Model both children as particles, with $g=9.8\ \text{m s}^{-2}$ .
Find the magnitude of the reaction of the pivot on the plank.2 marks
A non-uniform rod $AB$ of length $4$ m and mass $15$ kg is held horizontally in equilibrium by two vertical light strings attached at $A$ and $B$ . The tension in the string at $B$ is $88.2$ N. Take $g=9.8\ \text{m s}^{-2}$ .
A particle of mass $5$ kg is attached to the rod so that the tensions in the two strings are equal. Find the distance of the particle from $A$ .2 marks
A uniform beam $AB$ of length $5$ m and mass $50$ kg rests horizontally on two smooth supports at $C$ and $D$ , where $AC=1$ m and $DB=1$ m. A man of mass $60$ kg stands on the beam at $E$ , where $EB=0.5$ m. Model the man as a particle, with $g=9.8\ \text{m s}^{-2}$ .
Find the reaction of the support at $D$ on the beam.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).