Isolated main-sequence stars as massive as 10 to 12 times the mass of the Sun may still manage to avoid going supernova. Why?
A) because they can also have strong stellar winds
B) because about half that mass will be contained in the carbon core
C) because they would be classified as brown dwarfs
D) because these stars will eject at least 4 solar masses in the planetary nebula stage
E) because their masses will decrease as they fuse heavy elements into lighter elements in their cores
A
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An 20 cm-diameter horizontal steam pipe carries 1.66 kg/min of dry saturated steam at 120°C. If ambient air temperature is 20°C, determine the rate of condensate flow at the end of 3 m of pipe. Use an emissivity of 0.85 for the pipe surface. If heat losses are to be kept below 1 per cent of the rate of energy transport by the steam, what thickness of fiberglass insulation is required? The rate of energy transport by the steam is the heat of condensation of the steam flow. The heat of vaporization of the steam is 2210 kJ/kg.
GIVEN • A horizontal steam pipe in air • Pipe outside diameter (D) = 20 cm= 0.2 m • Mass flow rate of steam (ms) = 1.66 kg/min=0.0277 kg/s • Steam temperature (Ts) = 120°C =393 K • Ambient air temperature (T?) = 20°C= 293 K • Emissivity of pipe surface (?) = 0.85 • Heat of vaporization (hfg) = 2210 kJ/kg FIND (a) Rate of condensate flow (mc) at the end of 3 m of pipe. (b) Thickness of fiberglass insulation (S) to keep loss below 1% of the energy transport by steam ASSUMPTIONS • Steady state • Air is still • Thermal resistance of the convection in the pipe and of the pipe wall are negligible • The surroundings behave as an enclosure at T? • Insulation is foil covered, its emissivity ? 0.0 PROPERTIES AND CONSTANTS the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4) Thermal conductivity of fiberglass (ki) = 0.035 W/(m K) for dry air at the mean temperature of 70°C Thermal expansion coefficient (?) = 0.00291 1/K Thermal conductivity (k) = 0.0288 W/(m K) Kinematic viscosity (?) = 17.1*10-6 m2/s Prandtl number (Pr) = 0.71
A certain radioactive isotope placed near a Geiger counter registers 120 counts per minute. If the half-life of the isotope is one day, what will be the count rate at the end of four days?
A) 30 counts/min B) 15 counts/min C) 10 counts/min D) 7.5 counts/min E) 5 counts/min
The energy of motion is called
a. inertia. b. power. c. kinetic energy. d. potential energy.
Nylon is a polyamide; Dacron is a(n) ______________
Fill in the blank(s) with correct word