Given that a large sunspot, about 100× smaller than the Sun, is about the same size as our planet, how many Earths could fit inside the Sun's vast volume?
A) 100 B) 1,000 C) 10,000 D) 100,000 E) one million
E
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The heat loss from uninsulated hot water pipes installed in homes can be considerable and hence increases the overall energy cost of the home. Consider a 5-m-long section of such a pipe that has an outer diameter of 1.7 cm and a surface temperature of 75°C. If the room air temperature is 20°C, calculate the natural convection heat loss from the pipe section. If the radiation heat losses are to be included as well, determine its contribution as a percentage of the total pipe heat transfer rate; assume that the outer pipe surface has an emissivity of 0.7.
GIVEN
• Uninsulated hot water pipe dissipating heat to surrounding
• Emissivity (?) = 0.7
• Diameter of cylinder (D) = 1.7 cm= 0.017 m
• Surface temperature (Ts) = 75°C= 348 K
• Ambient air temperature (T?) = 20°C= 293 K
• Length of the cylinder (L)= 5 m
FIND
(a) Natural convection heat loss from pipe section.
(b) Contribution of radiation as percentage of
total pipe heat transfer rate.
SKETCH
ASSUMPTIONS
• Air is still
• Surface temperature is uniform and constant
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 47.5°C
Thermal expansion coefficient (?) = 0.00312 1/K
Thermal conductivity (k) = 0.02695 W/(m K)
Kinematic viscosity (?) = 18.27 × 10–6 m2/s
Prandtl number (Pr) = 0.71
For what kinds of stars are the masses of stars in the H-R diagram "orderly"? For what kinds of stars are they disorderly? In other words, could you guess the mass of a star from its location (luminosity, temperature) on the H-R diagram?
What will be an ideal response?
Buoyancy: A block of metal weighs 40 N in air and 30 N in water. What is the buoyant force on the block due to the water? The density of water is 1000 kg/m3.
A. 10 N B. 30 N C. 40 N D. 70 N
The terrestrial planets, ranked in order of decreasing atmospheric density, are
a. Venus, Earth, Mars, Mercury b. Venus, Mars, Earth, Mercury c. Mercury, Mars, Earth, Venus d. Mars, Venus, Mercury, Earth