engineering option

Question 1

how do you calculate the moment of inertia for a point mass?

Answer 1

I = mr^2

r= distance from axis of rotation (m)
m= mass (kg)
I= moment of inertia (kgm^2)

Question 2

define the moment of inertia (I) of a rigid extended body :

Answer 2

the resistance to a change of rotational motion , depending on the distribution of mass around a chosen axis rotation

Question 3

what units are moment of inertia measured in ?

Answer 3

kgm^2

Question 4

what is moment of inertia dependent on ?

Answer 4

the total mass (m)
how the mass is distributed about the axis of rotation(r)

Question 5

when can the moment of inertia of a body change ?

Answer 5

depending on its orientation relative to the axis of rotation

Question 6

what are the factors affecting the energy storage capacity of a flywheel

Answer 6

mass: as mass increases I increases

angular speed: rotational KE = the square of angular speed , if any speed increase so does RKE

friction: although efficient , stored energy can be lost to friction , reduced by - lubricating bearings , using bearings made of superconductors
shape of the flywheel

Question 7

what is the use of flywheels in machines

Answer 7

flywheels are heavy rotating discs used to store rotational kinetic energy and stabilise machine speed - they act as energy reservoirs
and are used in machines requiring short intense bursts of power

Question 8

Use of flywheels for smoothing torque and speed

Answer 8

the flywheel added will speed up or slow down over a period of time because of its inertia and as a result, the sharp fluctuations in torque are ‘smoothed’

Question 9

is power in an engine produced continuously?

Answer 9

it is not produced continuously, power is produced in the ‘power stroke’ or ‘combustion’ part of an engine cycle, so it is released in bursts
This causes an engine to produce a torque that fluctuates

Question 10

use of flywheels in production processes

Answer 10

Flywheels are used in machines to act as an energy reservoir, by storing and supplying energy when required

Question 11

what is the analogy between rotational and translational dynamics ?

Answer 11

they are directly analogous , where angular variables replace linear ones -
force - torque
mass - I
f=ma - torque = I x angular acceleration

Question 12

what is translation measured in ?

Answer 12

meters

Question 13

what is rotation measured in ?

Answer 13

radians

Question 14

angular displacement equation

Answer 14

Δθ=s/r
s= arc length
r= radius

Question 15

angular velocity equation

Answer 15

ω=Δθ/Δt

Question 16

si unit for angular displacement ?

Answer 16

radians

Question 17

what is a complete circle in radians ?

Answer 17

360 degrees = 2 pi radians

Question 18

typically which direction is positive and which is negative

Answer 18

anticlockwise is positive and clockwise negative

Question 19

what is the equation for angular acceleration ?

Answer 19

α=Δω/Δt

Question 20

what does this symbol mean ?
ω

Answer 20

angular velocity

Question 21

what does this symbol mean ?
α

Answer 21

angular acceleration

Question 22

how do you calculate (delta) Δ x?

Answer 22

(final - initial)

Question 23

what is uniform angular acceleration?

Answer 23

the constant rate of change of angular velocity , measured in rad s^-2

Question 24

equations for uniform angular acceleration

Answer 24

𝜔2=𝜔1 + 𝛼𝑡
𝜃=𝜔1𝑡 + 1/2 𝛼𝑡2

(2/4)

Question 25

how to calculate torque ?

Answer 25

𝜏=𝐹𝑟 (force x perpendicular distance) 𝜏=𝐼𝛼 (moment of inertia x angular acceleration)

Question 26

what is torque ?

Answer 26

the turning effect of a force

Question 27

what is torque measured in ?

Answer 27

newton meters (Nm)

Question 28

how is angular momentum calculated?

Answer 28

𝐿 = 𝐼𝜔 for rigid bodies (moment of inertia x angular velocity)

Question 29

what is the conservation of angular momentum ?

Answer 29

the conservation of angular momentum states that the total angular momentum of a system remains constant if no net external torque acts on it .

Question 30

what happens if an objects moment of inertia decreases ?

Answer 30

its angular velocity increases to conserve momentum

Question 31

what is the conservation rule ?

Answer 31

initial angular momentum = final angular momentum

Question 32

how do you calculate work done ?

Answer 32

W = Tθ T = torque

Question 33

how do you calculate power ?

Answer 33

P = Tw T = torque ω = angular velocity

Question 34

does frictional torque have to be taken into account in rotating machinery ?

Answer 34

yes , frictional torque is a resistive force in rotating machinery - directly opposing motion of other components - leading to reduced system efficiency

Question 35

how do you calculate power loss

Answer 35

P loss = torque friction x ω ω = angular velocity

Question 36

what is the first law of thermodynamics ?

Answer 36

Q = Δu + W Q = energy transferred to the system ( by heating) Δu = change in internal energy W = work done BY the system

Question 37

what is an adiabatic process ?

Answer 37

Q = 0 - a system that exchanges no heat - energy is transferred only as work

Question 38

work done by the system

Answer 38

W is positive , meaning that internal energy increases

Question 39

work done on the system

Answer 39

W is negative meaning that internal energy increases

Question 40

isothermal processes

Answer 40

systems temperature remains constant - which means no change in internal energy of gas

Question 41

how do you calculate work done per cycle ?

Answer 41

area of the loop

Question 42

how do you calculate the area of an irregular shape loop ?

Answer 42

counting squares - count number of squares inside the loop - calculate area of one square and multiply

Question 43

how do you calculate the area of a simple shape

Answer 43

area = L X W - p(v final - v initial) 0.5 x base x height

Question 44

work done at constant pressure

Answer 44

W = p ΔV

Question 45

what happens when a gas expands at constant pressure

Answer 45

work done BY the system is positive

Question 46

what happens when gas is compressed at constant pressure

Answer 46

work done ON the system is negative

Question 47

which way is an arrow denoting expansion pointing ?

Answer 47

to the right

Question 48

which way is an arrow denoting compression pointing ?

Answer 48

to the left

Question 49

overall efficiency

Answer 49

brake power / input power

Question 50

thermal efficiency

Answer 50

indicated power / input power

Question 51

mechanical efficiency

Answer 51

brake power / indicated power

Question 52

is it possible for engines to work only by using first principle of thermodynamics

Answer 52

it is impossible because some heat will always be transferred to the engine ( increasing its temp) if the engine temp. = heat source temp , no heat flows , no work done

Question 53

second law of thermodynamics

Answer 53

heat from heat source = QH some is transferred to work ( W) , some to heat sink which has a lower temp (Tc)

Question 54

how to calculate efficiency

Answer 54

W/QH = QH-Qc/QH Qc = heat from sink QH = heat from heat source

Question 55

how to calculate maximum theoretical efficiency

Answer 55

TH - Tc / TH

Question 56

can engines be 100 percent efficient

Answer 56

no it is physically impossible due to constraints of second law thermodynamic

Question 57

why are practical engines less efficient

Answer 57

laws of thermodynamics prevent 100 percent conversion of energy into work

Question 58

how do refrigerators work

Answer 58

removes as much heat as possible from a cold space cold space = inside fridge hot space = room

Question 59

how do heat pumps work

Answer 59

pumps the maximum possible heat from a cold space per June of work done cold space = environment used to heat rooms