Suppose you measure the brightness and period of a number of Cepheid variable stars in Galaxy A and Galaxy B. You ?nd that all the Cepheid variables in Galaxy A are approximately 25 times as bright (apparent brightness) as Cepheid variables with similar periods in Galaxy B. What can you conclude about the distances of these galaxies?
A) Galaxy A is 25 times as far away as Galaxy B.
B) Galaxy A is 5 times as far away as Galaxy B.
C) Galaxy B is 25 times as far away as Galaxy A.
D) Galaxy B is 5 times as far away as Galaxy A.
D) Galaxy B is 5 times as far away as Galaxy A.
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An educated scientific guess is a
A) hypothesis. B) theory. C) either of these D) neither of these
The bottom of a flat–bottomed aluminum boat has area = 4.0 m2 and mass = 120 kg. If two fishermen and their fishing gear with total mass of 240 kg are placed in the boat, how much lower will the boat ride in the water? (water density = 1.0 × 10^3 kg/m3)
a. 0.15 m c. 0.075 m b. 0.090 m d. 0.060 m
How does the energy of the cosmic microwave background compare to the energy radiated by all the stars and galaxies that ever existed?
A) They are very close to being equal. B) 73% cosmic background, 27% starlight. C) About ten times more from the Big Bang than from stars and galaxies. D) The starlight now dominates the background, as your eyes show clearly. E) We have no way of comparing matter and energy this way.
It is possible using the analogies between linear motion and rotational motion to write an expression for rotational kinetic energy. The formula for rotational kinetic energy (assuming ? is torque, ? is angular acceleration, I is rotational inertia, and ? is angular velocity) is
A. ½ I ?2. B. ½ ? ?2. C. ½ ? ?2. D. ½ I ?2.