a$)$ Define the following terms used in Engineering Mechanics.

$($i$)$ Plastic Deformation $($ii$)$ Strain Hardening Exponent

b$)$ What is strength of Materials and why is its study important to your field of specialization?

c$)$ State atleast two differences between brittle and ductile materials.

d$)$ From the stress $-$ strain curve, it is evident that within the elastic boundaries, engineering stress is proportional to

true stress. After the elastic limit$,$ engineering values and true values of stress are different. Give two reasons why

this is the case.