First Law of Thermodynamics: The gas in a perfectly insulated but flexible container does work at a rate of 13 W. At what rate is the internal (thermal) energy of the gas changing?
A. -13 W
B. 13 W
C. 0 W
D. 6.5 W
Answer: A
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Two billiard balls have velocities of 2.0 m/s and -1.0 m/s when they meet in an elastic head-on collision. What is the final velocity of the second ball after collision?
a. +2.0 m/s c. -0.5 m/s b. -1.0 m/s d. +1.0 m/s
A plane wall 15 cm thick has a thermal conductivity given by the relation k = 2.0 + 0.0005 T W/(m K) where T is in degrees Kelvin. If one surface of this wall is maintained at 150 °C and the other at 50 °C, determine the rate of heat transfer per square meter. Sketch the temperature distribution through the wall.
GIVEN
A plane wall
Thickness (L) = 15 cm = 0.15 m
Thermal conductivity (k) = 2.0 + 0.0005 T W/(m K) (with T in Kelvin)
Surface temperatures: Th = 150 °C Tc = 50 °C
FIND
(a) The rate of heat transfer per square meter (q/A)
(b) The temperature distribution through the wall
ASSUMPTIONS
The wall has reached steady state
Conduction occurs in one dimension
SKETCH
Which of these statements is true for the image formed by an object placed in front of a thin lens?
A. convex lenses never produce virtual images B. real images are always enlarged C. real images are always inverted D. virtual images are always inverted
Which of the following is not a method astronomers use to determine the physical conditions inside the Sun?
A) detecting solar neutrinos generated in the Sun's core B) measuring Doppler shifts to observe solar vibrations C) observing X-ray images of the solar interior using satellites D) building mathematical models that use the laws of physics E) both C and D