Which of the following statements is true in the context of radioactive elements?
A) The abundances of the daughter isotopes of radioactive elements in a rock gradually decrease.
B) The abundance of a radioactive element in a rock gradually decreases.
C) Uranium-238 has the longest half-life among all the other radioactive substances.
D) Potassium-40 has the longest half-life among all the other radioactive substances.
B
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A spacecraft is measured by an observer on the ground to have a length of 53 m as it flies toward the earth with a speed 1.7 × 108 m/s
The spacecraft then lands and its length is again measured by the observer on the ground, this time while the spacecraft is at rest on the launchpad. What result does he now get for the length? (c = 3.00 × 108 m/s)
How can astronomers measure the period of a planet's orbit?
A) by measuring the time between peaks in the star's velocity curve B) by timing the cycle of small changes in a stars position on the sky C) by measuring the time between repeated transits D) all of the above
A rocket can never go faster than the speed of its exhaust
Indicate whether the statement is true or false
What is the speed of the wave described by y(x,t) = A cos(x2 + 2Bxt +B2t2 )
A) B/2 B) B C) 2Bx D) B2 E) The function given is not a solution to the wave equation.