At what minimum rate is a 60.0-kg boy using energy when, in 8.00 s, he runs up a flight of stairs that is 10.0-m high?
A) 75.0 W
B) 735 W
C) 4.80 kW
D) 48.0 W
B
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Thin Lenses: How far from a converging lens of focal length 30 cm must an object be placed so the image will be virtual and 3.0 times as large as the object?
Fill in the blank(s) with the appropriate word(s).
Brown dwarfs are ____
a. stars with a very thick dust sphere around them, so they appear "brown" b. low mass M type stars with hundreds of planets c. an anomaly because they are extremely small but have relatively high temperature d. protostars that could not ignite the fusion of hydrogen at their core e. has a surface temperature of 2500 K by fusing hydrogen
Which of the following may explain the failure to observe Population III stars?
A. Population III stars had their surfaces contaminated by remnants of massive stars. B. We do not expect to observe Population III stars, because pure hydrogen and helium stars never formed. C. The first stars to be formed in the young Milky Way are too far away to be detected. D. None of these choices is correct.
When considering whether the density of the universe is above or below the critical density, what needs to be included in the measurement of density?
A) ordinary matter B) ordinary matter and dark matter C) ordinary matter, neutrinos, gravity waves and electromagnetic energy D) ordinary matter, dark matter and electromagnetic energy E) ordinary matter, dark matter, neutrinos, gravity waves, electromagnetic energy and dark energy