AP Physics C: Chapters 12 -13

The conditions that the sum of forces and the sum of the torques both vanish:

• hold for every solid body in equilibrium

• hold only for elastic solid bodies in equilibrium

• hold for every solid body

• are always sufficient to calculate the forces on a solid object in equilibrium

• are sufficient to calculate the forces on a solid object in equilibrium only if the object is elastic

• must be zero

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Three identical uniform rods are each acted on by two or more forces, all perpendicular to the rods. Which of the rods could be in static equilibrium if an additional force is applied at the center of mass of the rod?

• Only 1

• Only 2

• Only 3

• Only 1 and 2

• All three

The conditions that the sum of forces and the sum of the torques both vanish:

• hold for every solid body in equilibrium

• hold only for elastic solid bodies in equilibrium

• hold for every solid body

• are always sufficient to calculate the forces on a solid object in equilibrium

• are sufficient to calculate the forces on a solid object in equilibrium only if the object is elastic

A 160-N child sits on a light swing and is pulled back and held with a horizontal force of 100 N. The magnitude of the tension force of each of the two supporting ropes is:

• 60 N

• 94 N

• 120 N

• 190 N

• 260 N

To determine if a rigid body is in equilibrium the vector sum of the gravitational forces acting on the particles of the body can be replaced by a single force acting at:

• the center of mass

• the geometrical center

• the center of gravity

• a point on the boundary

• none of the above

The center of gravity coincides with the center of mass:

• always

• never

• if the center of mass is at the geometrical center of the body

• if the acceleration due to gravity is uniform over the body

• if the body has a uniform distribution of mass

A cylinder placed so it can roll on a horizontal table top, with its center of gravity above its geometrical center, is:

• in stable equilibrium

• in unstable equilibrium

• in neutral equilibrium

• not in equilibrium

• none of the above

A cube balanced with one edge in contact with a table top and with its center of gravity directly above the edge is in ________ equilibrium with respect to rotation about the edge and in ________ equilibrium with respect to rotation about a horizontal axis that is perpendicular to the edge.

• stable, stable

• stable, unstable

• unstable, stable

• unstable, unstable

• unstable, neutral

The diagram shows a stationary 5-kg uniform rod (AC), 1 m long, held against a wall by a rope (AE) and friction between the rod and the wall. To use a single equation to find the force exerted on the rod by the rope at which point should you place the reference point for computing torque?

• A

• B

• C

• D

• E