# Name: __________________ 1 Law of thermodynamics 1.Heat is added to a system, and the system does 26 J of work. If the internal energy increases by 7 J, how much heat was added to the system?

Mechanics

Oct 27, 2013 (4 years and 6 months ago)

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Name: __________________

1
st

Law of thermodynamics

1.

Heat is added to a system, and the system does 26 J of work. If the internal energy increases by 7 J, how
much heat was added to the system?

2.

The internal energy

of the gas in a gasoline engine’s cylinder decreases by 195 J.

If 52.0 J of work is done
by the gas, how much energy is transferred as heat? Is this energy added or removed from the gas?

3.

A 2.0 k
g quantity of water is held at constant volume in a pressure cooker and heated by a range element.
The system’s inte
rnal energy increases by 8.0 x 10
3

J. However, the pressure cooker is not well insulated,
and as a result, 2.0 x 10
3

J
of
energy is transferred to the surrounding air. How much energy is transferred
from the range element to the pressure cooker as heat?

4.

The internal energy of a gas decreases by 344 J. If the process is
adiabatic, how much energy is transferred
as heat? How much work is done on or by the gas?

5.

A steam engine’s broiler completely converts 155 kg of water to steam. This process
involves the transfer of
3.5 x 10
8

J as heat. If steam escaping through a
safety

valve does 1.76 x 10
8

J of work expanding against the
outside atmosphere, what is the net change in the internal energy of the water
-
steam system?

Name: __________________

Section Review:

1.

In the sys
tems listed below, identify where energy is transferred as heat and work and where changes in
internal energy occur. Is energy conserved in each case?

a.

The steam in a steam engine
consisting of a broiler, a firebox
, a
cylinder
, a piston, and a flywheel

b.

The drill bit of a power drill and a metal block into which a hole is being drilled

2.

Express the first law of thermodynamics for the following processes:

a.

Isothermal

b.

c.

Isovolumetric

3.

A compressor for a jackhammer expands the air in the hammer’s cy
linder at a constant pressure of 8.6 x
10
5

Pa. The increase in the cylinder’s volume is 4.05 x 10
-
4

m3. During the process 9.5 J of energy is
transferred out of the cylinder as heat.

a.

What is the work done by the air?

b.

What is the change in the air’s inte
rnal energy?

c.

What type of ideal thermodynamic process does this approximate?

4.

A mixture of fuel and air is enclosed in an engine cylinder fitted with a piston. The gas pressure is
maintained at 7.07 x 10
5

Pa as the piston moves slowly inward. If the
gas volume decreases by 1.1 x 10
-
4
m
3
and the internal energy of the gas increases by 62 J, how much energy is added or removed from the
system as heat?

5.

If a weather balloon in flight gives up 15 J of energy as heat and the gas within does 13 J of wor
k on the
outside air, by how much does its internal energy change?

6.

Why does opening the refrigerator door on a hot day not cause your kitchen to become cooler?

Name: __________________

1
st

Law of thermodynamics

1.

Heat is added to a system, and the system does 26 J of work. If t
he internal energy increases by 7 J, how
much heat was added to the system?

2.

The internal energy of the gas in a gasoline engine’s cylinder decreases by 195 J. If 52.0 J of work is
done by the gas, how much energy is transferred as heat? Is this ener
gy added or removed from the gas?

3.

A 2.0 kg quantity of water is held at constant volume in a pressure cooker and heated by a range
element. The system’s internal energy increases by 8.0 x 10
3

J. However, the pressure cooker is not well
insulated, a
nd as a result, 2.0 x 10
3

J of energy is transferred to the surrounding air. How much energy
is transferred from the range element to the pressure cooker as heat?

4.

The internal energy of a gas decreases by 344 J. If the process is adiabatic, how muc
h energy is
transferred as heat? How much work is done on or by the gas?

5.

A steam engine’s broiler completely converts 155 kg of water to steam. This process involves the
transfer of 3.5 x 10
8

J as heat. If steam escaping through a safety valve doe
s 1.76 x 10
8

J of work
expanding against the outside atmosphere, what is the net change in the internal energy of the water
-
steam system?

Name: __________________

Section Review:

1.

In the systems listed below, identify where energy is transferred as heat and work and where changes
in
internal energy occur. Is energy conserved in each case?

a.

The steam in a steam engine consisting of a broiler, a firebox, a cylinder, a piston, and a flywheel

b.

The drill bit of a power drill and a metal block into which a hole is being drilled

2.

Expr
ess the first law of thermodynamics for the following processes:

c.

Isothermal

d.

e.

Isovolumetric

3.

A compressor for a jackhammer expands the air in the hammer’s cylinder at a constant pressure of 8.6 x
10
5

Pa. The increase in the cylinder’s volume is 4.0
5 x 10
-
4

m3. During the process 9.5 J of energy is
transferred out of the cylinder as heat.

f.

What is the work done by the air?

g.

What is the change in the air’s internal energy?

h.

What type of ideal thermodynamic process does this approximate?

4.

A mixtur
e of fuel and air is enclosed in an engine cylinder fitted with a piston. The gas pressure is
maintained at 7.07 x 10
5

Pa as the piston moves slowly inward. If the gas volume decreases by 1.1 x 10
-
4
m
3
and the internal energy of the gas increases by 62 J,

how much energy is added or removed from the
system as heat?

5.

If a weather balloon in flight gives up 15 J of energy as heat and the gas within does 13 J of work on the
outside air, by how much does its internal energy change?

6.

Why does opening the

refrigerator door on a hot day not cause your kitchen to become cooler?