Mechanics - Materials (Module 11)

Question 1

Define the density of a substance

Answer 1

This is the mass per unit volume

Question 2

Define Hooke’s Law

Answer 2

This states that the force needed to stretch a spring is directly proportional to the extension of the spring from its natural length

Question 3

What happens if a spring is stretched beyond it’s elastic limits?

Answer 3

It does not regain its initial length when the force applied to it is removed

Question 4

How do you calculate the elastic potential energy stored in a stretched spring?

Answer 4

Ep = 1/2 F x the change in L = 1/2 K x the change in ( L )^2

Question 5

Define tensile stress in the wire

Answer 5

Stress is defined as the force (or tension) per unit area of a material.

Question 6

Define tensile strain in the wire

Answer 6

Strain is defined as extension per unit length.

Question 7

What is the equation for Young’s modulus?

Answer 7

( TL ) / ( A x change in L) (Tensile stress / Tensile strain)

Question 8

Define plastic deformation

Answer 8

This is the deformation of a solid beyond its elastic limit.

Question 9

What is the difference between a brittle material and a ductile material?

Answer 9

Brittle material = snaps without any noticeable yield (e.g glass)
Ductile material = can be drawn into a wire (copper is more ductile than steel)

Question 10

Define the limit of proportionality

Answer 10

This is the limit beyond which, when a wire or a spring is stretched, its extension is no longer proportional to the force that stretches it

Question 11

What Is the equation for density?

Answer 11

Density= Mass/Volume

Question 12

What is the formula for A (cross section area of a cylinder I.e wire/cable)

Answer 12

(3.14 X d^2) ÷4