Eng physics

Question 1

Angular displacement (theta)

Answer 1

The angle through which a point has been rotated.

Question 2

Angular velocity (w)

Answer 2

Vector quantity describing: The angle a point rotates through per second (w=theta/t)

Question 3

Angular acceleration

Answer 3

The rate of change of angular velocity (acc=w/t)

Question 4

What is the gradient of an angular displacement-time graph?

Answer 4

Angular velocity (w)

Question 5

What is the gradient of an angular velocity- time graph?

Answer 5

Angular acceleration

Question 6

What happens then an angular displacement-time graph DOESNT have a constant angular acceleration

Answer 6

Curve is no longer proportional

Question 7

First law of thermodynamics

Answer 7

Q=/_\U + W
Q-energy transferred to system by heating (If energy transferred away from system, -neg)

U is increase in internal energy, sum of potential and kinetic energies of all the particles in a system

-W is work done by system (work done by gas).
If work is done on the gas eg by compressing it, W will be -neg.

Question 8

Isothermal change

Answer 8

Constant temperature

p1V1=p2V2

Question 9

Adiabatic Processes

Answer 9

IN adiabatic processes Q=0
WHERE NO HEAT IS LOST OR GAINED BY SYSTEM
U=-W Means any change in internal energy of the system is caused by work done by the system
p1V1=p2V2 * is adiabatic constant

Question 10

Internal energy

Answer 10

Only depends on temperature

Question 11

Work done

Answer 11

W=p/_\v

Question 12

Processes at a constant volume

Answer 12

Do no work. (W=0)

Question 13

Isothermal compression and adiabatic compression on graph:

Answer 13

Isothermal LOWER down than adiabatic

Question 14

Four stroke engine: PETROL

Answer 14

Induction-

• Piston starts at top and moves down, increasing vol. of gas above it
• Sucks in a mixture of fuel and air through inlet valve, PRESSURE REMAINS CONSTANT IN THIS STEP (below atmospheric)

Compression

• Inlet valve closed
• Piston moves back up cylinder and does work on the gas, increasing pressure
• Just before piston is at the end of this stroke, spark plug creates a spark which ignites mixture
• Temp and Pressure suddenly increase at ALMOST CONSTANT VOLUME

Expansion
(Hot air fuel gas mixture expands and does work on piston, moving it downwards
-Work done by the gas to expand, is more than the work done to compress as now at a higher temp. (NET OUTPUT OF WORK)
Just before piston reaches bottom of stroke, exhaust valve opens and PRESSURE REDUCES

Exhaust
Piston moves up cylinder and burnt gas leaves through exhaust valve
-Pressure remains almost constant

Question 15

Four stroke diesel engine:

Answer 15

Induction:
Only air is pulled into cylinder

Compression: Air compressed to reach a temp high enough to ignite diesel, before end of stroke diesel is sprayed into cylinder

Expansion and exhaust strokes are same