Mechanics assumptions

Question 1

Rod

Answer 1

mass concentrated along a line
no thickness
rigid

Question 1

Particle

Answer 1

mass is concentrated at single point, rotational forces and air resistance can be ignored

Question 2

Lamina

Answer 2

mass distributed across flat surface

Question 3

Uniform body

Answer 3

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

Question 4

Light object

Answer 4

zero mass
tension same at both ends of light string

Question 5

Inextensible string

Answer 5

acceleration is the same in objects concentrated by a taut inextensible string

Question 6

smooth surface

Answer 6

assume no friction between the surface and any object on it

Question 7

Rough surface

Answer 7

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

Question 8

Wire

Answer 8

treated as one dimensional

Question 9

Smooth and light pulley

Answer 9

pulley has no mass
tension is the same on either side of the pulley

Question 10

bead

Answer 10

moves freely along a wire or string
tension is the same on either side of the bead

Question 11

Peg

Answer 11

dimensionless and fixed,
can be rough or smooth as specified in question

Question 12

Air resistance

Answer 12

modeled as being negligible

Question 13

Gravity

Answer 13

assume that all objects with mass are attracted towards the earth.
Earth’s gravity is uniform and acts vertically downwards
g i constant and taken as 9.8