What is true of spring tides?
A) The third quarter Moon would be high overhead at dawn.
B) The difference between low and high tides would be greatest.
C) There would be one high and one low tide each day.
D) The Moon's phase will be first quarter.
E) The difference between low and high tides would be smallest.
B
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In a nonlinear elastic material, the ratio of the increment in applied stress to the increment in strain measured at the total strain is the _____________modulus.
Fill in the blank(s) with the appropriate word(s).
Angular Momentum: A 5.0-m radius playground merry-go-round with a moment of inertia of 2000 kg ? m2 is rotating freely with an angular speed of 1.0 rad/s. Two people, each of mass 60 kg, are standing right outside the edge of the merry-go-round and suddenly step onto the edge with negligible speed relative to the ground. What is the angular speed of the merry-go-round right after the two people have stepped on?
A. 0.20 rad/s B. 0.40 rad/s C. 0.60 rad/s D. 0.80 rad/s E. 0.67 rad/s
Light-emitting diodes or LEDs are currently perhaps the most energy-efficient lighting systems. Finned surface heat sinks are used to cool high-intensity LED lighting that are used for spot and/or track lighting systems. A typical circular pin-fin heat sink is shown in the figure, and it is desirable that the fin-base temperature be less than 115°C to ensure efficient performance and longer life of the LED lamp. The fins are made of cold-forged, high-conductivity aluminum (k = 210 W/m K). Each pin has a diameter of 4 mm and a length of 40 mm. If the surrounding air is at 22°C, and it has a convection heat transfer coefficient of ch = 10 W/(m2 K), determine the temperature distribution in the fin, considering convection from the fin tip and the heat transfer rate from the fin. Model it
as a one-dimensional system, use a minimum of 9 nodes (including the ones at the base and tip) or more in your numerical scheme, and determine the effect of extra nodes. Compare the results with the one-dimensional fin analysis of Chapter 2. Also, if 90 such fins are evenly distributed on a 50-mm-diameter circular base, what is the maximum heat transfer rate that is dissipated by this heat sink so that the base temperature is less than 115°C? In a typical LED lamp, approximately 70% of the electric power (or wattage) is dissipated as heat (the remainder 30% is useful light). Determine the maximum power of the lamp, in watts, for which this heat sink is used.
GIVEN
• Light emitting diodes
• Fin base temperature (T0)= 1150C
• Surrounding air temperature (T?)= 220C
• Convection heat transfer coefficient ( ch )= 10 W/(m2 K)
• Thermal conductivity (k)=210 W/(m K)
• Fin diameter (d)= 4 mm = 0.004 m
• Fin length (L)= 40 mm =0.04 m
• Number of nodes (N)=9
FIND (a) Temperature distribution in the fin considering convection from fin tip
(b) Heat transfer rate from the fin.
(c) Maximum heat transfer rate dissipated by 90 such evenly distributed fins
(d) Maximum power of lamp in watts.
SKETCH
A point on the rim of a 0.30-m radius rotating wheel has a tangential speed of 4.0 m/s. What is the tangential speed of a point 0.10 m from the center of the same wheel?
a. 1.0 m/s c. 2.7 m/s b. 1.3 m/s d. 8.0 m/s