Exam Revision

Question 1

How do you find the direction of angular velocity?

Answer 1

Using the RH rule.

If 2 things are rotating in the same direction, their angular velocity directions will also be in the same direction

Question 2

What are alternative units for angular momentum?

Answer 2

Original: kg m^2 s^-1

Alternatives: Nms, Js^-1

Question 3

What is the thermal resistance?

What are the units?

Answer 3

Heat flow through multiple objects. This can be in series or in parallel.

Units: Kelvins/Watt (K/W)

Question 4

What is the R factor?

Answer 4

The thermal resistance per unit area

m^2 K/W

Question 5

Is the time taken for heat flow the same for parallel and series?

Answer 5

No, it will be different

Question 6

What does a lower thermal resistance mean?

Answer 6

The higher the heat flow rate, meaning it will take less time to carry heat from one place to another

Question 7

What happens to the kinetic energy and momentum in a totally inelastic collision?

Answer 7

Kinetic energy isn’t conserved, while momentum is always conserved

Question 8

Is total mechanical energy still conserved in a totally inelastic collision?

Answer 8

Yes, only the kinetic energy isn’t conserved.

This just means that the energy has been gained potential energy or internal energy.

Question 9

What is the change in internal energy in a cyclic process?

Answer 9

0, because it ends up where it started

Question 10

What is Q when W is +ve (compressing)

Answer 10

Q is -ve, so heat is removed from the system

Question 11

What is Q when W is -ve (expanding)

Answer 11

Q is +ve, so heat is added to the system

Question 12

How do you find an unknown volume along an isotherm?

Answer 12

In an isothermal process, temperature is constant so pV=nRT is constant along the isotherm

Use p1V1 = p2V2 to solve

Question 13

What equation do you use to find power when given force and velocity?

Answer 13

P = Fv

Derive from P=E/t = Nm/t = W/t = Fd/t = Fv

Question 14

In a static equilibrium problem, where do you place the object/person to find the max weight it can be before the system falls over? Why?

Answer 14

Take it at the top of the log/ladder as this is where the greatest torque will be

Question 15

In uniform circular motion, why is the angular frequency the same as the angular velocity?

Answer 15

Because the time to complete one revolution is the angular frequency and it takes the angular speed to complete that path

2pi F = 2pi / T

Question 16

How are angular frequency and angular velocity different?

Answer 16

Angular frequency is a constant and does not change with time, where angular velocity does

Question 17

What is the phenomena that occurs in rolling motion without slipping?

Answer 17

The velocity from the surface’s POV is 0, meaning that the kinetic energy is made up of both rolling and transnational energies

Question 18

How is angular momentum different to the rotational inertia of an object?

Answer 18

p = mv <> L = I(omega)

Rotational inertia is an object’s resistance to rotate, where angular momentum is the torque required to change rotational movement.

Question 19

What changes the angular momentum of an object?

Answer 19

The torque

Question 20

Why is angular frequency a constant?

Answer 20

Because omega=2pi/T, where the frequency is taken within 2pi radians

Question 21

When work is done on the system, is the work positive or negative?

Answer 21

Positive because it’s being compressed

Question 22

When work is done by the system, is the work positive or negative?

Answer 22

Negative because it’s expanding

Question 23

Will the individual thermal resistance of 2 identical blocks be the same? How does this compare to the total thermal resistance in parallel vs in series?

Answer 23

Yes R will be the same for both

However, RT changes depending on how the blocks are oriented, meaning the heat flow will change.

Question 24

Is heat flow greater in parallel or in series? What does this depend on?

Answer 24

Mostly greater in parallel because surface area x2 and length 1/2, so will be around 1/4 the thermal resistance in series, therefore 4 times as fast

Question 25

How do you find the heat added to the system when given heat flow rate and time?

Answer 25

Multiply the two together to get heat in Joules

Question 26

How to you find the work done in a cyclic process that returns back to its original position?

Answer 26

Find the area enclosed by the graph.

*Be careful as the sign will be different depending on the direction of the process

Question 27

What can you determine in terms of the gauge pressure if the mass of 2 fluids are the same? Why?

Answer 27

It means that the gauge pressure of both will be the same.

This is because the gauge pressure depends on the

Question 28

What is Archimedes’ principle?

Answer 28

The buoyant force is given by the weight of the displaced fluid

Question 29

How do you determine the volume of an object if you know its mass and the apparent weight?

Answer 29

First find the buoyant force

Then from there you can find the volume displaced. If it’s completely submerged it’s equal to the volume of the object

Solve for density using p=m/V