Answer the following statement(s) true (T) or false (F)
1. Consider a rectangular book. The book is (approximately) symmetric (in the sense defined in the chapter) for rotations around an axis that is perpendicular to its face and goes through its center of mass.
2. The book is (approximately) symmetric for rotations around an axis that goes diagonally from one corner to the other.
1. TRUE
2. FALSE
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A 0.3-cm-thick aluminum plate has rectangular fins 0.16 x 0.6 cm, on one side, spaced 0.6 cm apart. The finned side is in contact with low pressure air at 38°C and the average heat transfer coefficient is 28.4 W/(m2 K). On the unfinned side water flows at 93°C and the heat transfer coefficient is 284 W/(m2 K). (a) Calculate the efficiency of the fins (b) calculate the rate of heat transfer per unit area of wall and (c) comment on the design if the water and air were interchanged.
GIVEN
FIND
(a) The fin efficiency (?f)
(b) Rate of heat transfer per unit wall area (q/Aw)
(c) Comment on the design if the water and air were interchanged
ASSUMPTIONS
Width of fins is much longer than their thickness
The system has reached steady state
The thermal conductivity of the aluminum is constant
SKETCH
An important reason that sedimentary rocks are economical is that they are porous and permeable. Natural gas, for example, collects in the pore spaces between the sediment grains within these rocks. Porosity is the amount of space between the grains within a rock. It can be quantified as the total volume of space between grains divided by the volume of grains. A low porosity means that there is little space, and a high porosity means that there is a lot of space. -Permeability is how much the pore spaces are connected. Fluid flows through rocks that are more permeable.
The image below is an illustration of two different rocks. These images are magnified to show the individual grains (dark gray) and pore spaces (light gray) that make up the rock. Study these images and select the statement that describes the correct comparison of the porosity and permeability of these two rocks.
A.) Rock A has a lower porosity and a lower permeability than Rock B.
B.) Rock A has a higher porosity and a lower permeability than Rock B.
C.) Rock A has a lower porosity and a higher permeability than Rock B.
D.) Rock A has a higher porosity and a higher permeability than Rock B.
The radius of the Moon's orbit is about ____ times larger than the radius of Earth
a. 0.6 b. 6 c. 60 d. 600 e. 6000
A 1000-turn toroidal solenoid has a central radius of 4.2 cm and is carrying a current of 1.7 A. What is the magnitude of the magnetic field inside the solenoid at the central radius? (?0 = 4? × 10-7 T ? m/A)
A) 81 mT B) zero C) 16 mT D) 8.1 mT E) 51 mT