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Work and Energy - Physics Exam Study Guide

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  • Can work be done on a system if there is no motion?
    No, because of the way work is defined.
  • How much work is done holding a 50-N object lifted 2.0 m vertically in place?
    0J
  • If you push twice as hard against a stationary brick wall, the amount of work you do
    remains constant at zero.
  • Does the centripetal force acting on an object do work on the object?
    No, because the force and the displacement of the object are perpendicular.

  • You throw a ball straight up. Compare the sign of the work done by gravity while a ball goes up and down.

    Work is - on the way up and + on the way down.

  • What does the area under the curve on a Force vs. position (F vs. x) graph represent?

    Work.
  • If the net work done on an object is positive, then the object's kinetic energy
    increases.

  • Car J moves twice as fast as Car K, and Car J has half the mass of car K. What is the kinetic energy ratio of car J to car K?

    2 to 1.
  • If a brick moves at 3 m/s and a pebble at 5 m/s with the same kinetic energy, what is the mass ratio brick to pebble?
    25 to 9.
  • What does the quantity mgy represent?
    The gravitational potential energy of the object.
  • Is it possible for a system to have negative potential energy?
    Yes, since the choice of the zero of potential energy is arbitrary.
  • If a 0.200-kg mass stretches a spring 5.0 cm, what happens to the potential energy if another 0.200-kg mass is added?
    It becomes 4 times as much.
  • When is the total mechanical energy of a system constant?
    Only if conservative forces act.
  • Which object rises to a greater height sliding up a frictionless hill: a lightweight or a heavy object with equal speeds?
    They both slide to the same height.
  • A ball gains 30 J of kinetic energy dropping some distance with air resistance. How much gravitational potential energy did it lose?
    More than 30 J.
  • What is the correct SI unit of power?
    kg m²/s³.