A 3.0-kg mass moving in the positive x direction with a speed of 10 m/s collides with a 6.0-kg mass initially at rest. After the collision, the speed of the 3.0-kg mass is 8.0 m/s, and its velocity vector makes an angle of 35° with the positive x axis. What is the magnitude of the velocity of the 6.0-kg mass after the collision?
a. 2.2 m/s
b. 2.9 m/s
c. 4.2 m/s
d. 3.5 m/s
e. 4.7 m/s
b
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A standard 4 10 cm steel pipe (ID = 10.066 cm., OD = 11.25 cm) carries superheated steam at 650°C in an enclosed space where a fire hazard exists, limiting the outer surface temperature to 38°C. To minimize the insulation cost, two materials are to be used; first a high temperature (relatively expensive) insulation is to be applied to the pipe and then magnesia (a less expensive material) on the outside. The maximum emperature of the magnesia is to be 315°C. The following constants are known.
(a) Specify the thickness for each insulating material.
(b) Calculate the overall heat transfer coefficient based on the pipe OD.
(c) What fraction of the total resistance is due to (1) steam-side resistance, (2) steel pipe
resistance, (3) insulation (combination of the two), and (4) outside resistance?
(d) How much heat is transferred per hour, per foot length of pipe?
GIVEN
• Steam filled steel pipe with two layers of insulation
• Pipe inside diameter (Di) = 10.066 cm=0.10066 m
• Pipe outside diameter (Do) = 11.25 cm=0.1125 m
• Superheated steam temperature (Ts) = 650°C
• Maximum outer surface temperature (Tso) = 38°C
• Maximum temperature of the Magnesia (Tm) = 315°C
• Thermal conductivities
? High-temperature insulation (kh) = 0.1 W/(m K)
? Magnesia (km) = 0.076 W/(m K)
? Steel (ks) = 43 W/(m K)
• Heat transfer coefficients
? Steam side ( ci h ) = 500 W/(m2 K)
? Outside ( co h ) = 11 W/(m2 K)
• Ambient temperature (Ta) = 21°C FIND
(a) Thickness for each insulation material
(b) Overall heat transfer coefficient based on the pipe OD (c) Fraction of the total resistance due to
? Steam-side resistance
? Steel pipe resistance
? Insulation
? Outside resistance (d) The rate of heat transfer per unit length of pipe (q/L) ASSUMPTIONS
• The system is in steady state
• Constant thermal conductivities
• Contact resistance is negligible
SKETCH
Relative to an initial height, an object raised twice as high has a gravitational potential energy
A) half as much B) twice as much. C) four times as much. D) need more information
If a spinning star gets larger in diameter, what happens to its rotation rate?
A) It increases. B) It will not change. C) It decreases.
Dr. X claims that the Hubble constant is 20 km/s/million light-years while Dr. Y claims it is 24 km/s/million light-years. Which statement below automatically follows?
A) Dr. X concludes that the universe is expanding, but Dr. Y does not. B) Dr. X will conclude that the Andromeda Galaxy (a member of our Local Group) is moving away from us at a slower speed than will Dr. Y. C) Dr. X will conclude that the universe is older than will Dr. Y. D) Dr. X believes that the universe will someday stop expanding, while Dr. Y believes it will expand forever. E) Dr. X will conclude that the universe contains more mass than will Dr. Y.