PHY031-OQuiz-M01-W05-01

A water skier is pulled by a boat traveling with a constant velocity. Which one of the following statements is false concerning this situation?

• The water skier is in equilibrium.

• The net acceleration of the skier is zero m/s2.

• The net force on the skier is zero newtons.

• There is a net horizontal force on the skier in the direction the boat’s velocity.

• The net vertical force on the skier is zero newtons.

Which of the following actions will take place if an object in unstable equilibrium is slightly displaced?

• The object will move in the direction opposite that of the displacement.

• The object will stop moving as soon as it reaches a place of stable equilibrium.

• The kinetic energy will decrease.

• The potential energy will decrease.

Complete the following statement: When determining the net torque on a rigid body, only the torques due to

• internal forces are considered.

• external forces are considered.

• forces that are either parallel or perpendicular to the lever arms are considered.

• forces that form action-reaction pairs as in applying Newton’s third law of motion are considered.

• internal and external forces are considered.

An object, which is considered a rigid body, is in equilibrium. Which one of the following statements is false when determining the forces and torques acting on the object?

• The linear acceleration or the angular acceleration of the object may not be equal to zero.

• The location of the rotational axis is arbitrary. Therefore, it can be placed at any point on the object that is convenient.

• In placing an x-y coordinate system on the object, the +x direction is arbitrary and it can be directed toward any direction that is convenient.

• A free body diagram of the external forces acting on the object is useful in analyzing this situation.

• The sum of the torques due to external forces must equal zero N·m.

Which of the following is not a requirement of static equilibrium?

• The angular momentum of the object must be zero.

• The vector sum of all the external forces that act on the body must be zero.

• The linear momentum of the object must be zero.

• The vector sum of all the external torques acting on the body must be zero.

• All of the above are requirements of static equilibrium.

Consider the drawing. A small disk with a radius r shares an axis with a wheel of radius 4r. An object of mass M1 hangs from a rope that is attached and wrapped around the wheel as shown. Another object of mass M2 hangs from a rope that is attached and wrapped around the disk as shown. Which one of the following conditions must be true if this system is in equilibrium?

• M1 = M2

• M1 < M2

• M1 > M2

A block is sliding down a ramp at a constant velocity. Which one of the following statements is true?

• The block is not in equilibrium because the net forces on the block are not equal to zero newtons.

• The block is in static equilibrium.

• The block is not in equilibrium because the net torque on the block is not equal to zero N · m.

• The block is in equilibrium, but it is not in static equilibrium.

• The block is not in equilibrium because the linear momentum of the block is not equal to zero kg · m/s.

What are the SI units of the shear modulus?

• N/m²

• N • m²

• N/m

• N • m

• N/m³

Complete the following statement: Young's modulus cannot be applied to

• a bending beam.

• a compressed liquid.

• a stretched wire.

• a compressed rod.

• a stretched rubber band.

A box that is submerged below the surface of a liquid is observed to have a volume V2, which is smaller than the initial volume V1 when the box was in air above the surface. If we wish to determine the “stress” on the box, what additional information is needed?

• bulk modulus of the material from which the box is made

• mass of the box

• bulk modulus of the liquid

• shear modulus of the material from which the box is made

• Young's modulus of the material from which the box is made