Sunspots often appear in pairs
Indicate whether the statement is true or false
T
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________ occurs when most of the material collapsing to form a protostar has fallen into a disk around the star and a strong wind from the warm protostar ejects material from its poles
a. An emission nebula b. Hydrostatic equilibrium c. The proton-proton chain d. The thermonuclear fusion of hydrogen e. A bipolar outflow
Water at 20°C enters a 1.91-cm-ID, 57-cm-long tube at a flow rate of 3 gm/s. The tube wall is maintained at 30°C. Determine the water outlet temperature. What error in the water temperature results if natural convection effects are neglected?
GIVEN
• Water flowing through a tube
• Entering water temperature (Tb,in) = 20°C
• Tube inside diameter (D) = 1.91 cm = 0.0191 m
• Tube length (L) = 57 cm = 0.57 m
• Mass flow rate (m) = 3 gm/s = 0.003 kg/s
• Tube wall surface temperature (Ts) = 30°C
FIND
(a) The water outlet temperature (Tb,out)
(b) Percent error in water temperature rise if natural convection is neglected
ASSUMPTIONS
• Steady state
• Tube temperature is uniform and constant
• The tube is horizontal
SKETCH
PROPERTIES AND CONSTANTS
for water at 20°C
Specific heat (c) = 4182 J/(kg K)
Thermal conductivity (k) = 0.597 W/(m K)
Kinematic viscosity (?) = 1.006 × 10–6 m2/s
Prandtl number (Pr) = 7.0
Absolute viscosity (?b) = 993 × 10–6 (Ns)/m2
Thermal expansion coefficient (?) = 2.1 × 10–4 1/K At 30°C ?s = 792 × 10–6 (Ns)/m2
When we say that Jupiter is at opposition we mean that it
A) is behind the Sun as seen from Earth, so that it appears very close to the Sun in our sky. B) is at its greatest western elongation. C) it is at the point in its orbit where it is farthest from the Sun. D) appears on the opposite side of the sky from the Sun, so that it is on our meridian at midnight.
Two radio antennas are 130 m apart on a north-south line. The two antennas radiate in phase at a frequency of 3.6 MHz. All radio measurements are made far from the antennas
What is the smallest angle, reckoned east of north from midway between the antennas, at which constructive interference of two radio waves occurs? (c = 3.00 × 108 m/s) A) 50° B) 55° C) 45° D) 40° E) 35°