Dark matter is detectable in the coronae of ____
a. elliptical galaxies only
b. spiral galaxies only
c. irregular galaxies only
d. spiral and elliptical galaxies only
e. all galaxies
e
You might also like to view...
One method of storing solar energy for use during cloudy days, or at night, is to store it in the form of sensible heat in a rock bed. Suppose such a rock bed has been heated to 70°C and it is desired to heat a stream of air by blowing it through the bed. If the air inlet temperature is 10°C and the mass velocity of the air in the bed is 0.5 kg/(s m2), how long must the bed be in order for the initial outlet air temperature to be 65°C? Assume that the rocks are spherical, 2 cm in diameter, and that the bed void fraction is 0.5. (Hint: The surface area of the rocks per unit volume of the bed is (6/Dp)(1 –(?).)
GIVEN
Packed bed of rocks with air blowing through it
Initial temperature of rocks (Tr) = 70°C
Inlet air temperature (Ta,in) = 10°C
Mass velocity of air (m/A) = 0.5 kg/(s m2)
Outlet air temperature (Ta,out) = 65°C
Surface area per unit volume (As/V) = (6/Dp)(1 –(?) )
FIND
Length of bed required (L)
ASSUMPTIONS
Rocks are spherical with diameter (D) = 2 cm = 0.02 m
Void fraction of the bed (?) = 0.5
Rock temperature remains practically constant
SKETCH
Which represents v vs. t for a ball which is thrown straight up, reaches the top, and falls back down (but before it hits the ground)?
A. 
B. 
C. 
D. 
Except for the Local Group, galaxies seem to be isolated and randomly in space
Indicate whether the statement is true or false
A 60.0-Hz ac generator with a peak voltage of 110 V drives a series RC circuit with R = 10.0 ? and C = 300 ?F. The power factor, cos ?, is
a. ?1.00. b. ?0.749. c. +0.749. d. +0.834. e. +1.00.