EDEXCEL A LVL Maths year 2 moments/SRB/Slopes

what does uniform mean

The weight acts at the centre

what does non uniform mean

the weight does not act at the centre

what does it mean when something is on the point of tipping about point A?

all other reactions are now 0

what 3 things does modelling something as a beam mean

• only has 1 dimension (length)

• its mass is concentrated along a line

• It is rigid (can’t bend)

what is the order of calculation for horizontal beams

• resolve vertically

• take moments

what is the order of calculation for static rigid bodies

• resolve vertically

• resolve horizontally

• take moments (usually around the bottom)

In a static rigid body against a wall, if there is friction between the plane and the wall (where friction is vertical), will we resolve the friction so that we can use the friction in the moments calculation

yes

if you have lots of sin thetas and cos thetas in an equation (when doing a calculation), what should u do to make it easier / simpler

• (after cancelling through anything where u can e.g any unkown variable lengths)

• divide everything by cos theta

• as this will cancel some cos thetas and will turn the sin theta ones into tan thetas

for any “state what would happen to…” question, in SRB for example, what do u need to do before coming up with a hypothesis

do some sort of maths / calculations so that u can prove it to be the case

what does equilibrium mean in mechanics

all forces are balanced

what does it mean when there is acceleration

what equation do we use with acceleration

• forces are imbalanced (there is a resultant force)

• F = ma

does friction resist motion?

yes

what is the formula for friction

F_MAX = mew R

what are the bounds / limits of friction

can be anything from 0 up until (mew*R)

for what 3 cases does friction take its max value?

• limiting equilibrium

• constant velocity

• acceleration

for any sub questions, should you redraw a force diagram if anything changes?

yes

when dealing with forces on a slope (regular) what is the order of calculation?

• resolve perpendicular to the plane

• resolve parallel to the plane

should u draw big diagrams?

yes

for connected particles / pulleys on slope, what is the order of calculation

• use F = ma vertically (on the particle not on slope)

• resolve perpendicular to the plane

• use F = ma on particle on slope (using the resolved parallel to slope)

• then do simultaneous equations

for the first part of a connected particle on slope question, where do u draw tension?

ONLY away from the particle

• for the first part(s) of the question DO NOT label tension going to the particles (near the pulley). should only be 2 T’s if on a regular one

label where the tension would be in this part of a question to do with tensions from pulley

what is the equation used to calculate the resultant force (Tension) exerted on the pulley by a string

2Tcos(90-theta/2)

derive the equation used to calculate the resultant force (Tension) exerted on the pulley by a string

Do this question

a) mew = 0.25

b) = particle will slide down the plane

do this question

look at image for answers

do this question

all done in image

explain why the perp reaction on a plane from something it rests on (e.g a drum) is actually perpendicular

it is perpendicular because the drum/object is smooth

In what direction is the resultant force acting on a slope at point A (the bottom)

the same direction as the slope e.g the force at angle theta

For any question that asks how the normal reaction would change, what do u have to think abt

• how it affects the perpendicularly resolved forces

• how it affects the horizontally resolved forces

• how it affects the moments