Mechanics

Question 1

particle modelling assumptions

Answer 1

• mass of the object is concentrated at a single point

- rotational forces and air resistance can be ignored

Question 2

rod modelling assumptions

Answer 2

• mass is concentrated along a line
• no thickness
• rigid (does not bend or buckle)

Question 3

lamina modelling assumptions

Answer 3

mass is distributed across a flat surface

Question 4

uniform body modelling assumptions

Answer 4

• mass of the object is concentrated at a single point at the geometrical centre of the body - the centre of mass

Question 5

light object modelling assumptions

Answer 5

• treat object as having zero mass

- tension the same at both ends of a light string

Question 6

inextensible string modelling assumptions

Answer 6

• acceleration is the same in objects connected by a taut inextensible string

Question 7

smooth surface modelling assumptions

Answer 7

• assume that there is no friction between the surface and any object on it

Question 8

rough surface modelling assumptions

Answer 8

• objects in contact with the surface experience a frictional force if they are moving or are acted on by a force

Question 9

wire modelling assumptions

Answer 9

• treated as one-dimensional

Question 10

smooth and light pulley modelling assumptions

Answer 10

• pulley has no mass

- tension is the same on either side of the pulley

Question 11

bead modelling assumptions

Answer 11

• moves freely along a wire or string

- tension is the same on either side of the bead

Question 12

peg modelling assumptions

Answer 12

• dimensionless and fixed

- can be rough or smooth as specified in question

Question 13

air resistance modelling assumptions

Answer 13

• usually modelled as being negligible

Question 14

gravity modelling assumptions

Answer 14

• assume that all objects with mass are attracted towards the Earth
• Earth’s gravity is uniform and acts vertically downwards
• g is constant and is taken as 9.8m/s^2, unless otherwise stated in the question

Question 15

base SI units

Answer 15

mass - kg
length/displacement - m
time - s

Question 16

derived SI units

Answer 16

speed/velocity - m/s
acceleration - m/s^2
weight/force - N

Question 17

Using calculus to work out velocity from displacement

Answer 17

v = ds / dt

Question 18

Using calculus to work out acceleration from velocity or displacement

Answer 18

a = dv / dt = d^2s/dt^2

Question 19

Using calculus to work out velocity from acceleration

Answer 19

integrate acceleration

Question 20

Using calculus to work out displacement from velocity

Answer 20

integrate velocity