A 100 kg crate is attached to a rope wrapped around the inner disk as shown. A person pulls on another rope wrapped around the outer disk with force F to lift the crate
How much work is done by the person to lift the crate 2 m?
1.about 400 J
2.slightly less than 2,000 J
3.exactly 2,000 J
4.slightly more than 2,000 J
5.much more than 2,000 J
6.Impossible to determine without knowing F
7.Impossible to determine without knowing the radii
8.Impossible to determine without knowing the mass of the pulley
9.Impossible to determine for two or more of the reasons given in 6, 7, and 8 above
10.Impossible to determine for some other reason(s)
2,3,4,5
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In an experiment different wavelengths of light, all able to eject photoelectrons, shine on a freshly prepared (oxide-free) zinc surface. Which statement is true?
a. The number of photoelectrons emitted per second is independent of the intensity of the light for all the different wavelengths. b. The number of photoelectrons emitted per second is directly proportional to the frequency for all the different wavelengths. c. The maximum kinetic energy of the photoelectrons emitted is directly proportional to the frequency for each wavelength present. d. The maximum kinetic energy of the photoelectrons has a linear relationship with the frequency for each wavelength present. e. The maximum kinetic energy of the photoelectrons is proportional to the intensity of the light and independent of the frequency.
The element potassium should produce compounds most similar to those of
a. Tc. b. Na. c. Al. d. Sr.
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.