Dynamics and statics and materials

Question 1

Thinking distance

Answer 1

Distance travelled at constant speed whilst reacting/before braking

Question 2

Braking distance

Answer 2

Distance travelled under constant deceleration during braking

Question 3

Newton’s first law

Answer 3

A body wil continue in a state of rest or moving with a constant velocity unless acted on by an external resultant force

Question 4

Newton’s second law

Answer 4

The rate of change of an object’s linear momentum is equal to the resultant external force. The change in momentum takes place in the direction of the force

Question 5

Principle of conservation of momentum

Answer 5

Total linear momentum of a system remains constant providing that no external resultant force acts

Question 6

Describe and explain the shape of the force-extension graph for loading and unloading an elastic band

Answer 6

Gradient of line represents stiffness of material
Initially elastic band stiff as chains of rubber molecules are long and tangled
As more force applied, molecules untangle and align themselves parallel to each other
Gradient of line decreases
At higher force values, gradient increases again because bonds between atoms are being stretched
When unloading, chains of rubber molecules remain parallel to each other until they dissipate the heat energy, cool down and return to their original tangled arrangement
Difference in area between two graphs gives amount of heat energy dissipated

Question 7

Young’s modulus

Answer 7

Young’s modulus of a material is the ratio of tensile stress to tensile strain

Question 8

Necking can be caused by

Answer 8

Dislocation in planes of atoms
Impurity
Wick

Question 9

Moment définition

Answer 9

Force x perpendicular distance from the pivot to the line of action of the force

Question 10

Couple

Answer 10

Equal and opposite coplanar forces

Question 11

Moment of a couple is

Answer 11

Force x perpendicular distance between the lines of action of the forces