Exam Revision Flashcards
How do you find the direction of angular velocity?
Using the RH rule.
If 2 things are rotating in the same direction, their angular velocity directions will also be in the same direction
What are alternative units for angular momentum?
Original: kg m^2 s^-1
Alternatives: Nms, Js^-1
What is the thermal resistance?
What are the units?
Heat flow through multiple objects. This can be in series or in parallel.
Units: Kelvins/Watt (K/W)
What is the R factor?
The thermal resistance per unit area
m^2 K/W
Is the time taken for heat flow the same for parallel and series?
No, it will be different
What does a lower thermal resistance mean?
The higher the heat flow rate, meaning it will take less time to carry heat from one place to another
What happens to the kinetic energy and momentum in a totally inelastic collision?
Kinetic energy isn’t conserved, while momentum is always conserved
Is total mechanical energy still conserved in a totally inelastic collision?
Yes, only the kinetic energy isn’t conserved.
This just means that the energy has been gained potential energy or internal energy.
What is the change in internal energy in a cyclic process?
0, because it ends up where it started
What is Q when W is +ve (compressing)
Q is -ve, so heat is removed from the system
What is Q when W is -ve (expanding)
Q is +ve, so heat is added to the system
How do you find an unknown volume along an isotherm?
In an isothermal process, temperature is constant so pV=nRT is constant along the isotherm
Use p1V1 = p2V2 to solve
What equation do you use to find power when given force and velocity?
P = Fv
Derive from P=E/t = Nm/t = W/t = Fd/t = Fv
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?
Take it at the top of the log/ladder as this is where the greatest torque will be
In uniform circular motion, why is the angular frequency the same as the angular velocity?
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
How are angular frequency and angular velocity different?
Angular frequency is a constant and does not change with time, where angular velocity does
What is the phenomena that occurs in rolling motion without slipping?
The velocity from the surface’s POV is 0, meaning that the kinetic energy is made up of both rolling and transnational energies
How is angular momentum different to the rotational inertia of an object?
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.
What changes the angular momentum of an object?
The torque
Why is angular frequency a constant?
Because omega=2pi/T, where the frequency is taken within 2pi radians
When work is done on the system, is the work positive or negative?
Positive because it’s being compressed
When work is done by the system, is the work positive or negative?
Negative because it’s expanding
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?
Yes R will be the same for both
However, RT changes depending on how the blocks are oriented, meaning the heat flow will change.
Is heat flow greater in parallel or in series? What does this depend on?
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
