the boat and just touches the water. The

flinkexistenceΜηχανική

27 Οκτ 2013 (πριν από 4 χρόνια και 14 μέρες)

403 εμφανίσεις

The rope ladder of a boat hangs over the side of
the boat and just touches the water. The
ladder rungs are 8 inches apart. How many
rungs will be under the water when the tide
rises 3.5 feet?

A.
1 rung

B.
2 rungs

C.
5 rungs

D.
0

rungs

How much
heat

would need
to be added to a 2.5 kg
sample of water in order to
increase the temperature
from 35
o
C to 95
o
C?
(Remember Q
= mc
Δ
T)

c
water

= 4190 J/
kg
o
C

A.
366.6 kJ

B.
628.5 kJ

C.
995.1 kJ

D.
1361.8
kj

Because the rubber ball’s
temperature increased faster
than the banana dipped in LN2,
that means which had a higher
specific heat.

A.
The rubber ball

B.
The banana

C.
Both have the same

D.
Neither are capable for getting heat

Pre
-
AP Physics Unit 5:
Thermodynamics

“Thermodynamics”


Is derived from Greek meaning “movement of heat.”

The First Law of Thermodynamics


Official Definition:

When heat flows in or out of a system, the energy it
gains or loses is
equal

to the amount of heat transferred.


Or…
Heat = Energy

!


Is analogous to the Law of Conservation of Energy


We are now dealing with
Internal Energy

Temperature:


What is it?


How “Hot” or “Cold” a substance is.


Temperature represents the average

translational
kinetic energy

of the individual

particles in a system.


The Temperature Scales


Fahrenheit


water freezes at 32
o
F and boils at 212
o
F


Celsius


Water freezes at 0
o
C and boils


at 100
o
C


Kelvin


is based off of
Absolute Zero


Absolute Zero


So cold that all particles
stop moving
!


Total
energy

of the particles is 0.

Temperature:


Temperature Conversions


Celsius to Fahrenheit

𝑇
𝐹
=
9
5
𝑇
𝐶
+
32



Fahrenheit to Celsius

𝑇
𝐶
=
5
9
(
𝑇
𝐹

32
)



Celsius to Kelvin

𝑇
𝐾
=
𝑇
𝐶
+
273



Examples

A piece of metal is heated to 475
o
F
,
what is this temperature in Celsius?

A.
887
o
C


B.
246
o
C

C.
519
o
C

D.
-
27
o
C

The melting point of copper is
1073
o
C.

What is this
temperature in Kelvin?

A.
800 K

B.
1899 K

C.
578 K

D.
1346 K

Specific Heat Capacity


What is it?


The
resistance

to
change in temperature

of a substance.


The Equation:


Q = mc
Δ
T


Examples:

How much heat energy is
required in order to raise the
temperature of a 0.5 kg iron nail
from a temperature of 25
o
C to
80
o
C?

A.
5750 J

B.
18400 J

C.
12650 J

D.
24150 J

A 75 kg piece of a concrete
sidewalk on a sunny day will gain
about 650,000 Joules of heat
energy from the sun. By how
much will its temperature
increase on that day?

A.
25133333 K

B.
3.0 K

C.
16810 K

D.
.33 K

An iron pot
containing 5 kg of water at
an initial temperature of 23
o
C is placed
on a stove. If the stove applies 560,000
Joules of heat energy, what is the final
temperature of the water?

A.
49.7
o
C

B.
26.7
o
C

C.
3.7
o
C


D.
76.5
o
C

A cup of water (c=4190) and a
piece of metal (c=350) are both
left to sit out on a sunny day. By
the end of the day, which will
have a greater change in
temperature?

A.
water

B.
metal

C.
They will have same temperature

D.
I don’t know

The Second Law of
Thermodynamics


Official Definition:

Heat, of itself, never flows from a colder object to a
warmer object.


Energy always flows from
Hot to Cold


This law is also called the
Law of Entropy


What is Entropy?


The amount of
disorder

in a system


The universe is always moving towards more entropy


Examples:


Ice melting


Liquid water evaporating


It takes
Work

(energy) to decrease Entropy


Types of Heat Transfer


Conduction


Heat transfer between materials that are in direct contact

with each other.


Convection


Transfer in a fluid by movement of the substance itself.


Radiation


Energy transmitted by electromagnetic waves.


Phase Changes


The States of Matter:

Phase Changes


Types of Phase Changes:


Melting


Evaporation


Condensation


Boiling


Sublimation

Melting

Condensation

Evaporation

Boiling

Sublimation

Phase Changes


How do you change the melting point or boiling point of
a substance?


Add a solute


Change the pressure

Phase Changes


Energy During Phase Changes












What happens to the temperature of
water

as heat is
added?


It
Increases
.


What happens to the temperature
during

a phase change?


It remains
constant
.


Phase Changes


Latent Heat


Latent Heat of Fusion


The amount of energy required to change a unit mass of any
substance from a solid to a liquid (and vice versa).


Abbreviated L
f

(or
H
f
)


Latent Heat of Vaporization


The amount of energy required to change a unit mass from
liquid to gas (and vice versa).


Abbreviated
L
v

(or
H
v
)

L
v

L
f

Phase Changes


Latent Heat


Equation:




Q = mL


Where:

Q = heat added during phase change

m = mass of sample

L = Latent Heat (of fusion or vaporization)



Examples:


How much heat is required to boil 3.5
kg of water? (
L
v

=
2.26x10
6

J/kg
)

A.
7910 J

B.
.0001264 J

C.
.0000001264 J

D.
7910000J

An experiment is performed and
it is found that it takes 13.0 x 10
6

Joules of energy to melt 4.8 kg of
iron. What is the Latent Heat of
fusion for Iron?


A.
2.7 x 10
6

J/kg

B.
2.7 x 10
3

J/kg

C.
6.2 x 10
7

J/kg

D.
6.2 x 10
4

J/kg

Latent Heat of Fusion

L
f