If three samples have the half-lives listed below, which is the most radioactive?
A) a sample with a half-life of 20 minutes
B) a sample with a half-life of 20 hours
C) a sample with a half-life of 20 years
D) a sample with a half-life of 20 million years
E) none of the above
Answer: A
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Suppose you put a chocolate layer on pieces of candy. Compared with the amount of chocolate used to cover 1 pound of large pieces, if you cover 1 pound of smaller pieces you'll use
A) less chocolate. B) the same amount of chocolate. C) more chocolate. D) makes no difference
American power plants usually supply 120 V ac
(a) At what frequency is this voltage supplied? (b) What is the maximum voltage?
Starting from rest at t = 0, a 5.0-kg block is pulled across a horizontal surface by a constant horizontal force having a magnitude of 12 N. If the coefficient of friction between the block and the surface is 0.20, at what rate is the 12-N force doing work at t = 5.0 s?
a. 0.13 kW b. 0.14 kW c. 0.12 kW d. 26 W e. 12 W
If a vibrating object has a frequency of 8 cycles per second, what is its period?
a. 8 seconds. b. 1/8 second. c. 640 seconds. d. 1/640th of a second. e. 1280 seconds.