A vertical vector of 3 units combined with a horizontal vector of 4 units has a resultant of
A) 1 unit.
B) 5 units.
C) 7 units.
Answer: B
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Which statement about the Magellanic Clouds is false?
A) They contain regions of rapid star formation. B) They are companions of the Milky Way. C) They are close to the south pole of the sky. D) They are the two closest galaxies to us. E) They are both irregular galaxies.
The theory of special relativity
A) is based on a complex mathematical analysis. B) does not agree with electromagnetic theory. C) does not agree with Newtonian mechanics. D) has not been verified by experiment.
Why does the temperature of the corona rise with latitude? a. Atoms undergo fission when repelled by the corona
b. Atoms become neutralized as they dissipate in higher altitudes. c. Atoms within the corona become more ionized at higher altitudes. d. Atoms are forced upward from the chromosphere to the corona. e. Atoms are less excited as they move from the photosphere to the corona.
An electronic circuit board is the shape of a flat plate 0.3 m × 0.3 m in plan-form and dissipates 15 W. It is placed in operation on an insulated surface in a horizontal position or at an angle of 45 degrees to horizontal, in both cases; it is in still air at 25°C. If the circuit fails above 60°C, determine if the two proposed installations are safe.
GIVEN
• A flat plate with insulated back, horizontal or at an angle of 45 degrees in still air
• Plate size (s × s) = 0.3 m × 0.3m
• Heat generation rate (qG) = 15 W
• Air temperature (T?) = 25°C
• Maximum plate temperature (Ts) = 60°C
FIND
• If the two plate positions are safe
ASSUMPTIONS
• Radiative heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 43°C
Thermal expansion coefficient (?) = 0.00316 1/K
Thermal conductivity (k) = 0.0267 W/(m K)
Kinematic viscosity (?) = 17.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71