Suppose an artificial satellite has been put into circular orbit about the Earth, at a distance from the center of the Earth equal to 1/4 the distance from the Earth's center to the Moon's center. In terms of the Moon's period Tm, what will be the period of the satellite?
A. 8 Tm.
B. Tm/16.
C. Tm/8.
D. 16 Tm.
E. Tm.
Answer: C
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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
An ice skater has a moment of inertia of 5.0 kg ? m2 when her arms are outstretched, and at this time she is spinning at 3.0 rev/s. If she pulls in her arms and decreases her moment of inertia to 2.0 kg ? m2, how fast will she be spinning?
A) 7.5 rev/s B) 3.3 rev/s C) 10 rev/s D) 2.0 rev/s
On the Kelvin scale the temperature is proportional to the average kinetic energy of the atoms or molecules whose temperature is being measured
a. True b. False Indicate whether the statement is true or false
Which of these scientists pioneered the study of electricity?
A) Isaac Newton B) Galileo C) Benjamin Franklin D) all of the above