In the general theory of relativity, we assume the observer to be
A) moving at a significant fraction of lightspeed.
B) moving with constant velocity.
C) moving slowly compared to lightspeed.
D) at rest.
E) None of the above.
E
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How will high tides differ from their average values when the Moon is in its full phase?
A. They will be higher than average. B. They will be lower than average. C. They will not differ from average values significantly. D. There are no high tides when the Moon is full.
What is the frequency of 20-mm microwaves? (c = 3.0 × 108 m/s)
A) 100 MHz B) 400 MHz C) 15 GHz D) 73 GHz
A simple pendulum and a mass oscillating on an ideal spring both have period T in an elevator at rest. If the elevator now accelerates downward uniformly at 2 m/s2, what is true about the periods of these two systems?
A) Both periods would remain the same. B) Both periods would increase. C) Both periods would decrease. D) The period of the pendulum would increase but the period of the spring would stay the same. E) The period of the pendulum would decrease but the period of the spring would stay the same.
The heat transfer coefficients for the flow of 26.6°C air over a 1.25 cm diameter sphere are measured by observing the temperature-time history of a copper ball of the same dimension. The temperature of the copper ball (c = 376 J/(kg K), ? = 8928 kg/m3) was measured by two thermocouples, one located in the center, and the other near the surface. The two thermocouples registered, within the accuracy of the recording instruments, the same temperature at any given instant. In one test run, the initial temperature of the ball was 66°C and the temperature decreased by 7°C in 1.15 min. Calculate the heat transfer coefficient for this case.
IVEN
• A copper ball with air flowing over it
• Ball diameter (D) = 1.25 cm = 0.0125 m
• Air temperature (T?) = 26.6°C
• Specific heat of ball (c) = 376 J/(kg K)
• Density of the ball (P) = 8928 kg/m3
• Thermocouples in the center and the surface registered the same temperature
• Initial temperature of the ball (To) = 66°C
• Lapse time = 1.15 min = 69 s
• The temperature decrease (To – Tf) = 7°C
FIND
• The heat transfer coefficient ch
ASSUMPTIONS
• The heat transfer coefficient remains constant during the cooling period.
SKETCH
