Mechanics

Question 1

What are vector and scalar quantities?

Answer 1

A vector quantity is any physical quantity that has both magnitude and direction, scalar quantities only have magnitude

Question 2

Define the moment of a force

Answer 2

moment of a force = the force multiplied by the perpendicular distance from the line of action of the force to the pivot

Question 3

Define a couple

Answer 3

A pair of forces equal in magnitude, opposite in direction which are separated by a perpendicular distance. (moment of a couple = force x perp distance between the forces)

Question 4

Define Centre of Mass

Answer 4

The centre of mass of an object is defined as the point in a body where the whole weight appear to act

Question 5

State the principle of moments

Answer 5

for a body in equilibrium, the sum of the clockwise moments is equal to the sum of the anti clockwise moments about a point

Question 6

What is friction?

Answer 6

A force that opposes motion, contact friction is between solid surfaces, drag or fluid friction is a resistance experienced due to collisions with the molecules of the fluid

Question 7

Newtons first law

Answer 7

An object will remain at rest or continue moving at a constant velocity unless acted upon by an unbalanced force

Question 8

Define Inertia

Answer 8

The mass of a body is a measure of its inertia which is its resistance to change in its motion

Question 9

Newtons second law

Answer 9

The rate of change of momentum of an object is proportional to the resultant force on the object, and in the direction of the resultant force

Question 10

Newtons third law

Answer 10

When body A exerts a force on body B, body B exerts an equal and opposite force on body A

Question 11

Define linear momentum

Answer 11

The momentum of an object is defined as the product of mass and velocity

Question 12

Define impulse

Answer 12

The impulse of a force is the product of the force and the time for which the force acts

Question 13

What is the principle of conservation of momentum?

Answer 13

Within a closed system (where bo external forces apply) the total momentum in any specified direction remains constant

Question 14

Define an elastic collision

Answer 14

A collision in which the total kinetic energy is conserved

Question 15

Define an inelastic collision

Answer 15

A collision in which some or all of the kinetic energy is transferred to other forms, for example, heat and sound energy

Question 16

Define energy

Answer 16

Energy is the capacity to do work

Question 17

State the principle of conservation of energy

Answer 17

Energy cannot be created or destroyed only transferred

Question 18

Define power

Answer 18

Power is the rate of doing work or rate of energy transfer

Question 19

Define density

Answer 19

Density is the mass per unit volume of a substance

Question 20

State Hookes law

Answer 20

The extension is directly proportional to the force applied provided the elastic limit is not exceeded

Question 21

Define tensile stress

Answer 21

the tensile force per unit cross sectional area

Question 22

Define tensile strain

Answer 22

the ratio of extension to original length

Question 23

Define young modulus

Answer 23

The ratio of stress to strain and is constant for a specific material

Question 24

Describe a ductile material

Answer 24

Can be drawn out into wires or battered into sheets, show large plastic deformation - copper, gold, iron

Question 25

Describe a brittle material

Answer 25

Elastic behaviour, up until a breaking point, show little or no plastic deformation before they fracture - glass, ceramics, cast steel

Question 26

Describe a polymer

Answer 26

polymers behave differently depending on their molecular structure e.g. polythene is easy to deform, perspex is more brittle