Final: Tuesday, April 29, 7pm, 202 Brookscommunity.wvu.edu/~miholcomb/Final Review, latest...
Transcript of Final: Tuesday, April 29, 7pm, 202 Brookscommunity.wvu.edu/~miholcomb/Final Review, latest...
Final: Tuesday, April 29, 7pm, 202 BrooksMakeup Monday April 28, 1pm, 437 White Hall
• 67% focused on this last section of the course
• Chapters 10.1-3, 11.1-2, 11.4-5, 13 (all), 14.1-5, 5.4
• There will also be problems from Chapters 1-7
(motion, forces, energy, momentum, rotation)
• Totaling 25 multiple choice questions
You should be able to convert between
K/C/F temperature scales
• Fahrenheit to Celsius
– TF = TC x (9/5) + 32
– TC = (TF - 32) x (5/9)
• Kelvin to Celsius
– TK = TC + 273.15
– TC = TK - 273.15
Not a simple factor conversion
∆∆∆∆TC = ∆∆∆∆TF *5/9
∆∆∆∆TC = ∆∆∆∆TK For more problems on Ch. 10 & 11, see lectures
and following problem solving day
You should be able to calculate the
amount of thermal expansion
• Length expansion
(thermometer)
∆L=αLo∆T
• Area expansion (ring)
∆A=γAo∆T
• Volume expansion
(basketball) ∆V=βV∆T
• Note: ∆T is in °C (or K)
• Note: γ =2α, β= 3α Thermometers rely on a thermal
expansion of a liquid (e.g. mercury)
Main Ideas in Chapter 11
You should be able to:
• Understand the ways to transfer heat (mostly conceptually except conduction)
• Calculate heat necessarily to raise the temperature or change the phase of a material
Extra Practice: 11.1, 11.3, 11.5, 11.7, 11.9, 11.15, 11.17, 11.25, 11.27, 11.33
Phase changes (e.g. solid to liquid)
When heating ice into water and then into steam the temperature does not go up uniformly
–Different slopes since cwater > cice
–Flat bits at phase changes
Time
Tem
pe
ratu
reice
water
steam
Melting Point
Boiling Point
Q = m c ∆∆∆∆Tc called the specific heat of a material
cwater = 4190 J/(kg K) - difficult to heatcice = 2090 J/(kg K)
Applying constant heat per second
mLv
mLf
Lf<Lv
https://www.youtube.com/watch?v=lTKl0Gpn5oQ
Transferring heat energy
• 3 mechanisms
– Conduction
• Heat transfer through material (rods, windows, etc.)
– Convection
• Heat transfer by movement of hot material (hot air, hot
liquid while cooking)
– Radiation
• Heat transfer by light
(sun, fire, tanning bed)
Rate of heat flow
(Conduction)
Energy flows from higher temp. to lower temp. (0th law)
Rate of energy transfer (P=power) depends on
– Temperature difference (TH-TC)
– Area of contact (A) and length (L) over which heat flows
– Thermal conductivity of the material (k)
• k (copper) = 385 W/(m K) good conductor
• k (air) =0.02 W/(m K) good insulator
• Higher k means more heat flow
- P in Watts, Q in Joules, t in seconds
L
TTkA
t
Q CH −=
∆=P
L
L
Main Ideas in Chapter 13
You should be able to:
• Understand Simple Harmonic Motion (SHM)
• Determine the Position, Velocity and Acceleration over time
• Find the Period and Frequency of SHM
• Relate Circular Motion to SHM
Extra Practice: C13.1, C13.3, C13.11, 13.1, 13.3, 13.5, 13.9, 13.11, 13.17, 13.19, 13.21, 13.23, 13.25, 13.27, 13.31
Period and Frequency Independent of Amplitude
• Period of a spring
– The period (T) of a mass on a spring is dependent upon the
mass m and the spring constant k
• Frequency
– The frequency, ƒ, is the number of complete cycles or
vibrations per second; units are s-1 or Hertz (Hz)
k
m2T π=
T
1ƒ =
• The angular velocity is related to the frequency
• The angular velocity/speed (or angular frequency)gives the number of radians per second
m
kƒ2 =π=ω
Graphical
Representation
of Motion
When x is a maximum or
minimum, velocity is zero
When x is zero, the speed is
a maximum (slope of x)
Acceleration vs. time is the
slope the of velocity graph.
When x is max in the
positive direction, a is max
in the negative direction
Velocity as a Function of Position
• Conservation of Energy allows a calculation of the
velocity of the object at any position in its motion
– Speed is a maximum at x = 0
– Speed is zero at x = ±A
– The ± indicates the object can be traveling in either
direction
( )2 2kv A x
m= ± −
2
212
212
21 kAkxmv =+
22
max
2
212
max21
Am
kv
kAmv
=⇒
=
More Ideas in Chapter 13
You should be able to:
• Understand the pendulum
• Determine different kinds of waves
• Find the wavelength, frequency and speed of a wave
• Damped Oscillations
The Simple Pendulum
xL
mgF −=
Since restoring force is proportional
to negative of displacement,
pendulum bob undergoes SHM.
Effective “spring constant” is
keff = mg/L
effk
mT π2=
g
LT π2=
spring pendulum
Pendulum
If a pendulum clock keeps perfect time at the
base of a mountain, will it also keep perfect
time when it is moved to the top of the
mountain? If not, will it run faster or slower?
No, g is slightly smaller at higher
altitude.
g
LT π2=
T will be bigger so it will take longer
to complete an oscillation.
Types of Waves
traveling wave
Transverse
Longitudinal
fv λ=
Are you on the right wavelength?
6 m/s 2 m
If the wave below has a velocity of 6 m/s, answer the following:
What is the wavelength?
What is the wave’s period?
What is the wave’s frequency?
2 m
T= λ/v = 2 m/(6 m/s) = 0.333 s
f =1/T = 1/0.333s = 3 Hz
fT
v λλ
==
Main Ideas in Chapter 14
You should be able to:
• Explain how a vibrating object
affects the nearby air molecules
to produce sound waves
• Calculate the speed, intensity
and decibels of sound
A man shouts and
hears his echo off a
mountain 5 seconds
later. How far away
is the mountain?
Speed of sound ~343m/s at room temperature
Compare to thunder
Determining distance
with echoes
One of the loudest sounds on Earth was made by the
volcanic eruption of Krakatoa in Indonesia in August
of 1883. At a distance of 161 km, the sound had a
decibel level of
180 dB. How far
away from the
source would
you be to not
experience pain
(<120 dB).
θθθθ = 35°
m= 12 kg
D = 3m
A 12 kg block slides 3 m from rest down a
frictionless ramp with an incline angle of 35°
before being temporarily stopped by a spring
with spring constant k=30,000 N/m. By how
much is the spring compressed when the block
stops?
How should we
approach this
problem?
A spring with spring constant 300 N/m is
attached to an object whose mass is 2.0 kg.
If the spring is initially stretched A=0.25 m,
what is the velocity of the object at x = 0, -A
and A/2?
2
212
212
21 kAkxmv =+
( )2 2kv A x
m= ± −