When a rock is held above the ground, we say it has some potential energy. When we let it go, it falls and we say the potential energy is converted to kinetic energy. Finally, the rock hits the ground. What has happened to the energy?
A) The energy goes into the ground and, as a result, the orbit of the earth about the Sun is slightly changed.
B) The energy goes to producing sound and to heating the ground, rock, and surrounding air.
C) The rock keeps the energy inside it (saving it for later use).
D) It is lost forever. Energy does not have to be conserved.
E) It is transformed back into gravitational potential energy.
B
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Stars originate as large bodies of slowly rotating gas. Because of gravity, these clumps of gas slowly decrease in size. The angular velocity of a star increases as it shrinks because of
A. conservation of angular momentum B. conservation of linear momentum C. conservation of energy D. the law of universal gravitation E. conservation of mass
Friction: An object slides on a level floor. It slows and comes to a stop with a constant acceleration of magnitude 2.4 m/s2. What is the coefficient of kinetic friction between the object and the floor?
A. 0.24 B. 0.48 C. 0.12 D. It is impossible to determine without knowing the mass of the object.
Jill is farsighted and cannot see objects clearly that are closer to the eye than 80.0 cm. What is the focal length of the contact lenses that will enable her to see objects at a distance of 25.0 cm from her eyes?
A) +36.4 cm B) -36.4 cm C) -21.2 cm D) +21.2 cm E) +32.5 cm
On this map of Earth, which numbered circle represents the place where the Sun appears directly overhead at noon on the December solstice?
A) 3 B) 1 C) 2 D) 4 E) None of the answers are correct; the Sun can be directly overhead only on the equator.