In active galaxies, their central engines may be temporarily fed by:
A) a sudden surge of star formation.
B) a series of supernovae around the core.
C) the sudden collapse of the core into a supermassive black hole.
D) a close encounter with a neighbor galaxy.
E) the fusion of helium into carbon in their cores.
D
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What is the wave number for a wavelength of 600 nm?
A. 600 nm
B. 
C. 
D. 
E. 
The heat loss from the hairdryer duct enclosure was neglected. To a designer, while this may appear to be reasonable assumption it should really be checked bu order of magnitude calculations even if all the parameters are not known. In order to determine whether the heat loss from the exterior of the duct enclosure is neglected or not, assume a high surface emissivity of 0.8, an average surface temperature of 400C, and consider an estimate for natural convection coefficient at a high reasonable value. If the length of hair dryer is 20 cm, calculate the expected heat loss per unit length of the dryer duct, compare it with heat dissipation per unit length from the internal electrical heating, and comment on validity of negligible heat loss assumption.
GIVEN - High surface emissivity of 0.8, an average surface temperature of 400C - Length of the hear drier L=20 cm =0.2 m FIND - Expected heat loss per unit length of dryer duct - Compare it with heat dissipation per unit length from the internal electrical heating. ASSUMPTIONS - Steady state conditions prevail - Heat loss from outside of dryer duct is neglected. PROPERTIES AND CONSTANTS the air properties are Convection heat transfer coefficient for air (considering higher value) (hc)=20 W/(m2 K) Specific heat capacity(Cp)= 1.0049 kJ/kgK
Galileo found the rotation period of the Sun was approximately
A) a day. B) a week. C) a month. D) three months. E) a year.
For general projectile motion, the horizontal component of a projectile's velocity
A) is zero. B) remains a non-zero constant. C) continuously increases. D) continuously decreases. E) any of the above, depending on position.