As far as you look, there seems to be nothing at all. Even the nearest electron is light-years away. No matter how far you travel, you can find no solid matter, not even a single proton. It's as if all of the matter in the universe has disintegrated
You do, however, detect a few strong gravitational fields—probably due to supermassive black holes—at enormous distances from you. Where are you?
A) You are in the universe when it is 1040 years old.
B) You are in the universe when it is 10100 years old.
C) You are in the GUT era of the early universe during the period of inflation.
D) You are in the Planck Era of the early universe.
E) You are in the central regions of a quasar.
A
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The average Reynolds number for air passing in turbulent flow over a 2-m-long flat plate is 2.4 x 106. Under these conditions, the average Nusselt number was found to be equal to 4150. Determine the average heat transfer coefficient for an oil having thermal properties similar to those in Appendix 2, Table 18 at 30°C at the same Reynolds number and flowing over the same plate.
GIVEN
Turbulent flow of air over a flat plate
Average Reynolds number (ReL) = 2.4 x 106
Plate length (L) = 2 m
Average Nusselt number (Nu) = 4150
FIND
Average heat transfer coefficient
ASSUMPTIONS
Steady state
Fully developed turbulent flow
Transition from laminar to turbulent flow occurs at Rex = 5 x 105
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 18, for oil at 30°C
Thermal Conductivity (k) = 0.11 W/(m K)
Kinematic Viscosity (v) = 15.4 ? 10–6 m2/s
Thermal Diffusivity (a) = 707 ? 10–10 m2/s
Visible, luminous matter (such as the stars within galaxies) amounts to what percentage of the critical density (the density of mass-energy needed to make the geometry of the universe flat)?
A) 25 percent B) 50 percent C) less than 1 percent D) 10 percent
An electric generator transforms
A) chemical energy into electrical energy. B) electrical energy into mechanical energy. C) mechanical energy into electrical energy. D) direct current into alternating current. E) alternating current into direct current.
A coil of 150 turns of wire is in the form of a circle, carries a current of 63 mA, and sits in the center of a dipole magnet that produces a uniform magnetic field of strength 1.5 T. The torque on the coil has a maximum value of 0.25 Nm. What is the radius of the coils?
A. 9.2 cm B. 13 cm C. 0.56 cm D. 7.5 cm