Living matter has 1.3 × 10-10% of its carbon in the form of 14C which has a half-life of 5730 yr. A mammoth bone has a 300-g sample of carbon separated from it, and the sample is found to have an activity of 20 decays per second
How old is the bone? A)
15,000 yr
B)
10,900 yr
C)
11,500 yr
D)
7,600 yr
E)
6,400 yr
B
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Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?
A) Supermassive black holes existed only when the universe was young, and no longer exist today. B) Active galactic nuclei can form only at large distances from the Milky Way. C) Active galactic nuclei exist tend to become less active as they age. D) The jets seen in many active galactic nuclei must cause them to move far away from us.
An open freight car rolls friction-free along a horizontal track in vertically pouring rain. As water accumulates in the car, its speed
A) increases. B) decreases. C) doesn't change.
The most accurate way of finding the distance to some very far away stars might be by observing
A. the rate of variation in their luminosity. B. their motion relative to nearby stars. C. their orbiting planets. D. the variation in their position in the night sky on successive nights.
Car A rear ends Car B, which has twice the mass of A, on an icy road at a speed low enough so that the collision is essentially elastic. Car B is stopped at a light when it is struck. Car A has mass m and speed v before the collision. After the collision
a. each car has half the momentum. b. car A stops and car B has momentum mv. c. car A stops and car B has momentum 2mv. d. the momentum of car B is four times as great in magnitude as that of car A. e. each car has half of the kinetic energy.