2. (A) A mass connected to an ideal spring is displaced from the equilibrium pos
ID: 1417512 • Letter: 2
Question
2. (A) A mass connected to an ideal spring is displaced from the equilibrium position by a distance x and released. Which one of the following statements concerning elastic potential energy is FALSE? Select one:
(a) The elastic potential energy has the SI unit of Joule
(b) The elastic potential energy is zero at certain times
(c) The elastic potential energy is a maximum when the displacement x is zero
(d) The elastic potential energy is converted into kinetic energy as the mass moves toward the equilibrium position
(B) A skydiver is suspended from a parachute, at a height of 2000 m above the surface of the Earth. She has a constant velocity downwards. Which one of the following statements concerning the forces acting on the skydiver is FALSE? Select one:
(a) The gravitational force is opposed by a friction force due to air resistance.
(b) The gravitational force and the friction force due to air resistance act in opposite directions.
(c) The magnitude of the friction force due to air resistance is less than the magnitude of the gravitational force.
(d) The friction force due to air resistance is a non-conservative force
(C) Which one of the following statements is TRUE? Select one:
(a) If an object is in equilibrium, there may be individual forces acting on it, but the vector sum of these forces must be zero.
(b) If an object is in equilibrium, then no individual forces are acting on it.
(c) If an object is in equilibrium, the individual forces acting on it must be mutually perpendicular.
(d) If an object is in equilibrium, then it must be at rest.
Explanation / Answer
2. (A) option (c) The elastic potential energy is maximum when the displacement x is zero.
This is because the elastic potential energy is maximum at maximum displacents. It is zero when x is zero.
(B). Option (c) The magnitude of the friction force due to air resistance is less than the magnitude of the gravitational force.
Since the skydiver is moving with a constant velocity then the net force acting on the skydiver should be zero. Which means that the friction force due to air resistance is equal and opposite to the gravitational force.
(C). Option (a) If an object is in equilibrium, there may be individual forces acting on it, but the vector sum of these forces must be zero.
Equilibrium position means that the net force acting on a system must be zero(not necessarily at rest).
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