Mechanics - Chapter 8 - Modelling in Mechanics

Question 1

when k=10m the ball passes through the net so the model is not valid for k>0 as the ball would’ve gone through/past the net so there would be possibly new forces acting on the ball - outside of what the model can predict (model used only for until it passes the net)

Question 2

particle -
dimensions of object negligible
assume mass acts at a single point. rotational forces/effects of any external forces and air resistance can be ignored

Question 3

rod - all dimensions but one are negligible, like a pole or beam
assume mass is concentrated along a line. no thickness. rigid (doesnt bend/buckle)

Question 4

Lamina - object with area but negligible thickness, like a sheet of paper
assume mass is distributed across a flat surface

Question 5

uniform body - mass is distributed evenly
assume mass concentrated at a single point at the geometrical centre of the body - the centre of mass

Question 6

light object - mass small compared to other masses, like a string or pulley)
assume treat object as having zero mass, tension is the same at both ends of a light string

Question 7

inextensible string - string that doesnt stretch under load
assume acceleration is the same in objects connected by a taut (tense) inextensible string

Question 8

inextensible string - string that doesnt stretch under load
assume acceleration is the same in objects connected by a taut (tense) inextensible string

Question 9

smooth surface
assume there is no friction between surface and any object on it

Question 10

rough surface - if surface is not smooth, it is rough
assume objects in contact with surface experience a frictional force if they are moving/acted on by a force

Question 11

wire - rigid thin length of metal
assume treated as one-dimensional

Question 12

smooth and light pulley (all pulleys are)
assume pulley has no mass, tension is the same on either side of the pulley

Question 13

bead - particle with a hole in it for threading on a wire or string
assume moves freely along a wire or string, tension is the same on either side of the bead

Question 14

peg - a support from which a body can be suspended or rested
assume dimensionless and fixed, can be rough or smooth

Question 15

air resistance - resistance experienced as an object moves through the air
assume usually modelled as being negligible, ignore frictional effects on the object due to air resistance

Question 16

gravity - forces of attraction between all objects, acceleration due to gravity = g = 9.8 ms-2
assume all objects w/ mass are attracted towards Earth
-Earth’s gravity is uniform & acts vertically downwards
- g is constant and = 9.8ms-2 unless otherwise stated in question