Modelling assumptions

Question 1

particle

Answer 1

dimensions of object are negligible
mass of object conc. at single point
rotational forces + air resistance ignored

Question 2

rod

Answer 2

all dimensions but one negligible (like pole)
mass con. along line
no thickness
rigid (can’t bend/buckle)

Question 3

lamina

Answer 3

area but negligible thickness (paper)

mass distributed across a flat surface

Question 4

uniform body

Answer 4

mass is distributed evenly

mass of object conc. at single point at geometrical centre of body (centre of mass)

Question 5

light object

Answer 5

small mass (like string/pulley)
treated with zero mass
same tension at both ends of light string

Question 6

inextensible string

Answer 6

string that doesn’t stretch under load

acceleration same in objects connected by taut inextensible string

Question 7

smooth surface

Answer 7

assume no friction between surface and objects in contact

Question 8

rough surface

Answer 8

not smooth (lol)
objects while moving in contact will experience frictional force

Question 9

wire

Answer 9

rigid thin length of metal

treated as 1D

Question 10

smooth and light pulley

Answer 10

all pulley considered smooth and light
no mass
tension same on either side of pulley

Question 11

bead

Answer 11

particle with hole in it for threading with wire/string
moves freely along wire/string
tension same on either side of bead

Question 12

peg

Answer 12

a support from which a body can be suspended or rested
dimensionless
fixed
can be rough or smooth (specified)

Question 13

air resistance

Answer 13

resistance experienced as inject moves through air

negligibility specified in question

Question 14

gravity

Answer 14

force of attraction between all objects
acceleration due to gravity denied by g
assume all objects with mass attracted towards Earth
Earth’s gravity uniform and acts vertically downwards
g = 9.8m s^-2 unless stated otherwise