The focal length of a convex mirror is
A. positive
B. negative
C. zero
D. infinity
B. negative
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Why were telescopes with very large, thin mirrors not built 50 years ago?
What will be an ideal response?
Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole. The black hole is surrounded by an accretion disk. Sometime within the next million years or so, the civilization's planet is likely to be doomed because
A) the red giant will probably supernova within the next million years. B) jets of material shot out of the accretion disk will shoot down their planet. C) the red giant star, which provides most of energy the civilization needs to exist, will soon be destroyed in the accretion disk. D) tidal forces from the black hole will rip the planet apart. E) the planet's orbit will gradually decay, as it is sucked in by the black hole.
Suppose that the maximum rate of change of current in a "high power" transmission line is 104 A/s. How large a coil (area) placed 10. meters from the line would have 120. volts (max) induced in it?
A) 6. × 103 m2 B) 2. × 105 m2 C) 6. × 105 m2 D) 2. × 103 m2 E) 6. × 104 m2
How much heat energy is needed to change 10 kg of water at 50°C to steam at 120°C?
A) 4.2 × 105 J B) 2.3 × 107 J C) 4.2 × 106 J D) 3.6 × 106 J E) 2.5 × 107 J