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 1, when gravity assembles the protostar from a collapsing cloud?
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.
A) Its surface temperature and luminosity increase.
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You put one ear on a steel railroad track while your friend a distance of 400 m away taps on the rail with a stone. You will hear the sound through the steel rail in _________ and through the air where the speed of sound is 344 m/s in _______
a. 0.08 s b. 0.5 s c. 1.2 s d. 2.4 s
Physical Pendulum: A thin hoop is supported in a vertical plane by a nail. What should the radius of the hoop be in order for it to have a period of oscillation of 1.00 s? The moment of inertia of a hoop of mass M and radius R about a point on its rim is 2MR2.
A. 0.0154 m B. 0.0621 m C. 0.124 m D. 0.1876 m E. 0.248 m
Radioactivity Basics: In ?- decay, the number of neutrons in the nucleus is
A. decreased by 1. B. decreased by 2. C. increased by 1. D. increased by 2. E. remains unchanged.
Suppose the ends of a 30-m-long steel beam are rigidly clamped at 0°C to prevent expansion. The beam has a cross-sectional area of 30 cm2 . What force against the clamps does the beam exert when it is heated to 40°C? (?Steel = 1.1 × 10^?5/°C, Ysteel = 20 × 10^10 N/m2)