Homer says that we can safely use nuclear power because all radioactive nuclei are gone after two half-lives. Marge says that only the decay rate is zero after two half-lives. Which one, if either, is correct, and why?
a. Homer, because half of the nuclei disintegrate in each half-life.
b. Marge, because the number of decays per unit time is halved in each half-life.
c. Homer, because it's safe to handle radioactive substances after two half-lives.
d. Both, because when all nuclei disintegrate the decay rate is also zero.
e. Neither, because one quarter of the nuclei are left after two half-lives.
e
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Gravity obeys an inverse square relation. This statement implies that the force due to gravity between two masses
a. will increase as the distance between the two masses increases. b. will decrease as the square of the distance between the two masses increases. c. will cause the two masses to move away from each other. d. will cause the two masses to move in a straight line. e. will cause the two masses to orbit each other.
Equilibrium: Two blocks, A and B, are being pulled to the right along a horizontal surface by a horizontal 100-N pull, as shown in the figure. Both of them are moving together at a constant velocity of 2.0 m/s to the right, and both weigh the same. 
Which of the figures below shows a correct free-body diagram of the horizontal forces acting on the lower block, B?
A. 
B. 
C. 
D. 
E. None of these diagrams is correct.
A tightrope walker with a mass of 60.0 kg stands at the center of a rope which was initially strung horizontally between two poles. His weight causes the rope to sag symmetrically, making an angle of 4.80° with the horizontal
What is the tension in the rope? A) 359 N B) 589 N C) 1760 N D) 2470 N E) 3520 N
Prior to decoupling, all matter was ________, with free electrons and nuclei
Fill in the blank(s) with correct word