The oxidation of iron to rust is a problem structural engineers need to be concerned about, but the oxidation of aluminum to aluminum oxide is not so much of a problem. Why?
A) Since aluminum is so light and inexpensive, it is easily replaced when corroded.
B) Aluminum oxide is insoluble in water and thus forms a protective coating that prevents continued oxidation of the aluminum.
C) Aluminum oxide is even stronger than aluminum.
D) The oxidation of aluminum is a very slow reaction, taking hundreds of years before any structural changes are noticed.
Answer: B
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Four of the five answers listed below are aspects of the scientific method. Select the exception
a. observation b. hypothesis c. experimentation d. philosophy e. conclusion
Magnetic Field of a Current Loop: A circular metal loop of radius 10 cm and three long straight wires carry currents of I1 = 60 A, I2 = 20 A, I3 = 70 A, and I4 = 30 A, as shown in the figure. Each of the straight wires is 20 cm from the center of the loop. The axes are shown in the figure, with the +z-axis coming out of the paper. What is the z component of the resultant magnetic field at the center of the loop? (?0 = 4? × 10-7 T ? m/A)
A. -360 ?T B. +360 ?T C. -40 ?T D. +40 ?T E. -170 ?T
How does a rocket take off?
A) Its rocket engines push against the launch pad, propelling the rocket upward. B) It converts mass-energy to kinetic energy. C) It achieves lift from its wings in the same way that airplanes do. D) Hot gas shoots out from the back of the rocket and, by conservation of momentum, the rocket moves in the opposite direction. E) The hot rocket exhaust expands the air beneath the rocket, propelling it forward.
Hubble's law is the major basis for the concept that the universe is
a. static. b. evaporating. c. contracting. d. expanding.