A__________is an otherwise normal spiral galaxy with an unusually bright, small core that fluctuates in brightness
A) pulsar
B) blazar
C) Seyfert galaxy
D) Markarian galaxy
C
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Plants use energy from the sun to produce nutrients. Plants are therefore:
a. consumers b. reproducers c. producers d. decomposers e. developers
A boy jumps with a velocity of magnitude 20.0 m/s at an angle of 25.0° above the horizontal. What is the horizontal component of the boy's velocity?
A) 18.1 m/s B) 15.6 m/s C) 8.45 m/s D) 12.6 m/s E) 9.33 m/s
A boat is floating in a small pond. The boat then sinks resting on the bottom, but the pond is so shallow that part of the boat is not submerged. What happens to the level of the pond?
a. It increases. b. It decreases. c. It stays the same. d. In some cases it would decrease, in others it would stay the same. e. In some cases it would increase, in others it would stay the same.
A long 1-cm-diameter electric cable is imbedded in a concrete wall (k = 0.13 W/(m K)) which is 1 m*1 m, as shown in the sketch. If the lower surface is insulated, the surface of the cable is 100°C and the exposed surface of the concrete is 25°C, estimate the rate of energy dissipation per meter of cable.
GIVEN
A long electric cable imbedded in a concrete wall with cable diameter (D) = 1 cm = 0.01 m
Thermal conductivity of the wall (k) = 0.13 W/(m K)
Wall dimensions are 1 m by 1 m, as shown in the sketch below
The lower surface is insulated
The surface temperature of the cable (Ts) = 100°C
The temperature of the exposed concrete surfaces (To) = 25°C
FIND
The rate of energy dissipation per meter of cable (q/L)
ASSUMPTIONS
The system is in steady state
The thermal conductivity of the wall is uniform
Two dimensional heat transfer
SKETCH
