The diagram above shows the life track of a 1 MSun protostar from the time it first begins to form until it reaches the main sequence, with four stages labeled. What is happening to the protostar's surface temperature and luminosity during Stage 2, when it is undergoing convective contraction, and its life track moves almost straight down on the HR diagram?
A) Its surface temperature and luminosity increase.
B) Its surface temperature remains the same and its luminosity decreases.
C) Its surface temperature and luminosity decrease.
D) Its surface temperature decreases and its luminosity increases.
E) Its surface temperature and luminosity remain the same.
B) Its surface temperature remains the same and its luminosity decreases.
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Two cars start at the same point, but travel in opposite directions on a circular path of radius R, each at speed v. While each car travels a distance less than 
, one quarter circle, the center of mass of the two cars
A. remains at the initial point. B. travels along a diameter of the circle at speed v' v. E. remains at the center of the circle.
An atom gains one extra electron. How does the resulting ion behave when it is near a positively charged transparency? How does the ion behave when it is near a negatively charged tissue?
A) The ion is attracted to the positively charged transparency, but repelled from the negatively charged tissue. B) The ion is repelled from both the transparency and from the tissue. C) The ion is repelled from the positively charged transparency, but attracted to the negatively charged tissue. D) The ion is attracted to both the transparency and to the tissue.
The similarity that Newton recognized between a falling apple and the moon was
A) the force on both is directed toward Earth's center. B) both have an acceleration that is directed toward the center of Earth. C) Both of the above. D) Actually there is no important similarity between these two. E) None of the above.
A horizontal disk with moment of inertia I1 rotates with angular speed ?1 about a vertical frictionless axle. A second horizontal disk, with moment of inertia I2 drops onto the first, initially not rotating but sharing the same axis as the first disk. Because their surfaces are rough, the two disks eventually reach the same angular speed ?. The ratio ?/?1 is equal to
1. I1 / I2 2. I2 / I1 3. I1 / (I1 + I2) 4. I2 / (I1 + I2)