A rock falls from a vertical cliff that is 4.0 m tall. At what speed will the gravitational potential energy of the rock-Earth system (relative to the base of the cliff) be equal to its kinetic energy? Assume that air has no effect on the motion of
the rock. A) 3.1 m/s
B) 4.4 m/s
C) 6.3 m/s
D) 8.9 m/s
E) 13 m/s
C
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Matthew pulls his little sister Sarah in a sled on an icy surface (assume no friction), with a force of 60.0 Newtons at an angle of 37.0° upward from the horizontal. If he pulls her a distance of 12.0 m, the work he does is
A) 0.333 kJ B) 720 J C) 575 J D) 433 J E) 185 J
Conventional automobile efficiencies cannot conceivably be higher than about 25%, even with perfect engineering. This is due to
A) the law of conservation of energy. B) frictional loses inside the car plus unburned hydrocarbons. C) the second law of thermodynamics. D) road friction. E) air resistance plus road friction.
Which of the following statements is an inference from a model (rather than an observation)?
A) The photosphere emits visible light. B) The Sun emits neutrinos. C) The Sun's core is gradually turning hydrogen into helium. D) The corona is hotter than the photosphere. E) The photosphere is made out of mainly hydrogen and helium.
An asteroid revolves around the Sun with a perihelion 0.5 AU and an aphelion of 7.5 AU. What is its period of revolution?
a. 4 years b. 8 years c. 16 years d. 32 years e. 64 years