A 2-kg rifle that is suspended by strings fires a 0.01-kg bullet at 200 m/s. The recoil velocity of the rifle is about
A) 0.001 m/s.
B) 0.01 m/s.
C) 0.1 m/s.
D) 1 m/s.
E) none of these
Answer: D
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A star can be a supernova:
A) in predictable cycles of decades. B) a few times, at unpredictable intervals. C) only if it can fuse iron in its core. D) before it reaches the main sequence, if it is massive enough. E) only once.
A spaceship leaves Earth and maintains a constant force by means of a nuclear engine. As the speed of the spaceship increases, an observer on Earth finds that relative to her the magnitude of the spaceship's acceleration is
A. 0. B. decreasing. C. constant. D. increasing. E. proportional to the kinetic energy of the spaceship.
A 60 kg boy standing on a skateboard with frictionless wheels and negligible mass throws a 3 kg ball straight up with a speed of 4 m/s. If the boy was at rest before the throw, his speed after the throw will be ________.
Fill in the blank(s) with the appropriate word(s).
There are samples of two different isotopes, X and Y. Both contain the same number of radioactive atoms. Sample X has a half-life twice that of Y. How do their decay rates compare?
a. X has a greater rate than Y. b. X has a smaller rate than Y. c. The rates of X and Y are equal. d. The rate depends on atomic number, not half-life.