Mechanics 8

Question 1

Particle (dimensions are negligible)

Answer 1

Mass concentrated at a single point
Rotational forces ignored
Air resistance ignored

Question 2

Rod (all dimensions but one are negligible)

Answer 2

Mass concentrated along a line
No thickness
Rigid (doesn’t bend or buckle)

Question 3

Lamina (has area but negligible thickness)

Answer 3

Mass distributed across a flat surface

Question 4

Uniform body (mass distributed evenly)

Answer 4

Mass of the object at a single point in geometrical centre of body (centre of mass)

Question 5

Light object (small mass)

Answer 5

Treat with mass=0
Tension the same at both ends of a light string

Question 6

Taut Inextensible string (doesn’t stretch under load)

Answer 6

Acceleration is the same for objects connected by it

Question 7

Smooth surface

Answer 7

No friction between it and any other object

Question 8

Rough surface

Answer 8

Objects in contact with it experience friction (if moving or acted on by a force)

Question 9

Wire (rigid thin length of metal)

Answer 9

Treated as one-dimensional

Question 10

Smooth and light pulley

Answer 10

Has no mass
Tension is the same on either side

Question 11

Bead (particle with a hole for threading)

Answer 11

Moves freely along a wire or string
Tension is the same on either side

Question 12

Peg (a support from which an object can be suspended)

Answer 12

Fixed dimensions
Can be smooth or rough

Question 13

Air resistance

Answer 13

Usually regligible