The apparent weight of a fish in an elevator is greatest when the elevator
a. moves downward at constant velocity.
b. moves upward at constant velocity.
c. accelerates downward. d. accelerates upward. e. is not moving.
D
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The great contribution of Nicholas Copernicus was to
A) create a detailed model of our solar system with the Sun rather than Earth at the center. B) prove that the Earth is not the center of the universe. C) discover the laws of planetary motion. D) discover the law of gravity.
A light oil flows through a copper tube of 2.6-cm-ID and 3.2-cm-OD. Air flows perpendicular over the exterior of the tube as shown in the following sketch. The convection heat transfer coefficient for the oil is 120 W/(m2 K) and for the air is 35 W/(m2 K). Calculate the overall heat transfer coefficient based on the outside area of the tube (a) considering the thermal resistance of the tube, (b) neglecting the resistance of the tube.
GIVEN
• Air flow over a copper tube with oil flow within the tube
• Tube diameters
? Inside (Di) = 2.6 cm = 0.026 m
? Outside (Do) = 3.2 cm = 0.032 m
• Convective heat transfer coefficients
? Oil h i= 120 W/(m2 K)
? Air h o= 35 W/(m2 K)
FIND
• The overall heat transfer coefficient based on the outside tube area (Uo), (a) considering the thermal resistance of the tube, and (b) neglecting the tube resistance
ASSUMPTIONS
• Uniform heat transfer coefficients
• Variation of thermal properties is negligible
SKETCH
PROPERTIES AND CONSTANTS
the thermal conductivity of copper (k) = 392 W/(m K) (at 127°C)
Standing Waves on a String: If a guitar string has a fundamental frequency of 500 Hz, which one of the following frequencies can set the string into resonant vibration?
A. 250 Hz B. 750 Hz C. 1500 Hz D. 1750 Hz
When a 10-N object is suspended at rest by two equally-taut vertical strands of rope, the tension in each strand is
A) less than 5 N. B) 5 N. C) more than 5 N. D) 10 N.