Mechanics and materials

Question 1

What shape do objects at equilibrium form in a scalar diagram?

Answer 1

Closed tip too tail

FORM DIAGRAMS TOO SOLVE FOR FORCES

Question 2

What are the SUVAT equations?

Answer 2

v= u + at
s = ut + 1/2 at^2
v^2 = u^2 + 2as
s = (u+v) / 2 *t

Question 3

When can you use SUVAT?

Answer 3

Constant acceleration

Question 4

How do you solve variable acceleration problems?

Answer 4

Energy changes

Question 5

How long does an object in a vacuum with a higher mass take compared to another of a lower mass and volume?

Answer 5

Where there is no air resistance, all objects in freefall will reach the ground at the same time

Question 6

Define a moment

Answer 6

The force multiplied by the perpendicular distance too the line of action of that force from the pivot that creates a turning effect

Question 7

When is a beam on a pivot at its toppling point?

Answer 7

The NCF is 0N

Question 8

What is a couple?

Answer 8

A pair of forces on the same object equal in magnitude and opposite in direction that don’t act in the same line separated my a distance x

Question 9

What is the moment of a couple?

Answer 9

F.x
(F is the magnitude of one of the identical forces)

Question 10

What is the centre of mass?

Answer 10

Where an objects weight is considered to act from

Question 11

When does an object topple?

Answer 11

The objects COM is above or past the objects pivot point

Question 12

NOT IN SPEC: What is the topple equation?

Answer 12

tan (toppling angle) = distance between COM and pivot / height of COM above ground

So, lower and wider is more stable as the same mass must be rotated around aa larger angle for it too topple requiring a larger moment.

Question 13

What are newtons laws of motion?

Answer 13

N1: An object in motion stays in motion unless a force acts upon it (inertia)
N2: Acceleration of a body is directly proportional too the force that acts upon it (constant mass)
N3: If A exerts a force on B, B will exert an equal and opposite force on A of the same type.

Question 14

What happens to the reading on a scale as a lift accelerates upwards?

Answer 14

The resultant force is upwards so the NCF>Weight. A Scale reads the NCF which is a constant but larger that the real weight of the person.

Question 15

Explain how an object reaches terminal velocity

Answer 15

Air resistance increases with velocity until the air resistance = weight force
A maximum value of velocity is reached

Question 16

How are air pressure and air resistance linked?

Answer 16

Increase air pressure, increase fluid density and increase in air resistance acting on any body

Question 17

What is work done in moving an object?

Answer 17

The energy transfer when a 1N force acts on an object over 1m (in the same direction)

Question 18

What is power?

Answer 18

The rate of energy transfer

Question 19

What is gravitational potential energy?

Answer 19

The work done against gravity in lifting a mass (m) by a height (h)

Question 20

What is the equation for conservation of linear momentum when two objects that collide are travelling in the same directions?

Answer 20

-m1(v1-u1) = m2(v2-u2)
Provided no external forces act upon it

Question 21

What is the equation for conservation of linear momentum when two objects that collide are head on?

Answer 21

m1(v1-u1) = m2(v2-u2)
Provided no external forces act upon it

Question 22

How do you solve an elastic collision for multiple unknowns?

Answer 22

Equation in terms of energy and an equation in terms of momentum and solve simultaneously

Question 23

What is Hooke’s law?

Answer 23

Force on a spring is directly proportion too its extension until its limit of proportionality

Question 24

How do springs attached too a load in parallel act?

Answer 24

Share the load equally when they have equal spring constants otherwise share the load by proportion

Question 25

How do springs attached too a load in series act?

Answer 25

They each carry the full load and add thee spring constants onto each other when equal

Question 26

What is the elastic limit?

Answer 26

The maximum stress a material can experience before it no loner returns too its original shape (begins plastic deformation)

Question 27

When is the limit of proportionality of a stress strain graph?

Answer 27

End of the linear region (stops following Hooke's law)

Question 28

Describe a brittle material graph

Answer 28

Large elastic region, small plastic (non linear)

Question 29

Describe a ductile material graph

Answer 29

Large plastic region, small elastic (linear)

Question 30

Describe a strong material graph

Answer 30

High UTS

Question 31

Describe a stiff material graph

Answer 31

High young's modulus / gradient

Question 32

What is necking?

Answer 32

Cross sectional area of a material decreases at the weakest point after UTS and so stress peaks again.

Question 33

Describe a tough material graph

Answer 33

Absorbs a lot of energy before breaking so a large area under the graph

Question 34

What is the area under a stress strain graph?

Answer 34

Elastic potential energy per unit volume

Question 35

What is hysteresis and what does it look like (Force extension graph)?

Answer 35

When elastic materials stretch their chains untangle and fold back down in a different order. Loading curve is different too the unloading curve.

Question 36

Compare the area under a loading curve versus unloading

Answer 36

Area unloading < loading as energy is usually lost too heat

Question 37

What is the yield point?

Answer 37

Where the atomic structure rearranges, a higher yield point means that a material is tougher as it can absorb more energy.