What evidence supports the assumption that a large number of living species disappeared about 65 million years ago due to a catastrophic impact?
A. the Chicxulub crater
B. the existence of a thin iridium layer of comparable geological age
C. the existence of a thin layer of soot of comparable geological age
D. All of these choices are correct.
Answer: D
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the magnetic field in the primed frame.
A. A B. B C. C D. D E. Toward the viewer F. Away from the viewer T. There is no field of this type.
How can we explain the fact that hydrogen Balmer lines are essentially absent in the hot O type and the cool M stars?
A. In O stars hydrogen is ionized and in M stars the electrons of hydrogen are in level 1, not level 2. B. O type stars do not contain hydrogen. C. In cool stars hydrogen combines to form large molecules. D. All of these choices are correct.
In a laboratory accident a work area is contaminated with radioactive material. Health physicists monitor the area during a 30-day period and, after correcting for the background rate, obtain the data shown in the table
Time (days) 0 2 6 11 19 30 Counts/min 1000 899 727 557 364 202 The accident occurred at t = 0. They determine that it will not be safe for workers to enter the area until the radioactivity level has dropped to 133 counts per minute. Of the choices listed below, which one is the earliest time that workers could safely return? A) 38 days B) 44 days C) 50 days D) 32 days E) 24 days
Two cylinders made of the same material roll down a plane inclined at an angle ? with the horizontal. Each travels the same distance. The radius of cylinder B is twice the radius of cylinder A. In what order do they reach the bottom?
a. A reaches the bottom first because it has the greater acceleration. b. A reaches the bottom first because it has a smaller rotatinal inertia. c. B reaches the bottom first because is experiences a larger torque. d. B reaches the bottom first because it travels a larger distance in one rotation. e. They both reach the bottom at the same time, because each has the same linear acceleration.