Thermodynamics -1st law
Useful equations
KE=½mv2
PE=mgh
ΔU=E2-E1=Q+W
1) Find the absolute temperatures in Kelvin for the following situations
a. Boiling point of water
b. Freezing point of water
c. Temperature at the beach (30°C)
d. Temperature on the ski slopes (-20°C)
2) Find the temperature in Celsius
a. Nitrogen becomes a liquid at 63 K
b. Steel becomes a liquid at 1478K
c. Gold becomes a liquid at 1336K
d. CO2 Solidifies at 195k
3) 60 kJ of work is needed to raise a body 90 m in the earth’s gravitational field where the local
acceleration of gravity is 9.55m/s2.
a. Find the mass of the body in kilograms
b. If the initial gravitational potential energy of the body was 10 kJ with respect to the
earths surface determine the final elevation of the body above the earth’s surface
4) Two hundred kilojoules of work are used to move a body at rest to a velocity of 200m/s
a. Determine the mass of the body in kg
b. If an additional 80kJ of work is done on the body, determine its new velocity
5) For each of the following cases of process involving a closed system, fill in the missing data. All
values are in units of
kJ
Case
A
B
C
D
E
F
Q
24
-8
18
-8
W
-15
E1
17
-14
26
28
13
-11
E2
-8
62
ΔU
7
-14
-18
20
12
6) A closed system changes state from 1 to 2 along path A. It is then returned back to state 1 by
one of three paths, X, Y, Z. Determine the missing data for Q and W
Path
A
X
Y
Z
Process
1 to 2
2 to 1
2 to 1
2 to 1
Q
-4
12
W
-7
8
-6
7) A gas expands slowly in a frictionless piston cylinder device from 0.1 to0.30 m3.
The process is described by P=7.4-40V+60V2, where P is in Bars and V is in m3.
The work done is W=7.4V-20V2+20V3.
a. Evaluate P and W for volumes 0.1, 0.2 and 0.3 m3
b. Determine the work done on the piston
8) For the system below find:
a. How much work does it take to go from point A to point B? (kJ)
b. If the temperature remains constant during this period, how much heat must be
transferred out of the system? (kJ)
P (kPa)
B (0.1, 500)
A (0.5, 100)
V (m3)