Torque and Rotation Review

Torque and Rotation Review

7.1 Rotational Kinematics

• Describes the motion of rotating objects.

• We assume a constant angular acceleration.

Multiple Choice

A disc rotates through 20 rotations in 5 seconds. If the disc starts from rest, what is the angular velocity?

• 5 rotations/s
• 100 rotations/s
• 4 rotations/s
• 10 rotations/s

Multiple Choice

What happens to the angular velocity when a figure skater brings in their arms?

• Increases her angular velocity

• Decreases her angular velocity

• Has no affect

Multiple Choice

Which statement is true about an object that is traveling in uniform circular motion?

• The speed of the object varies.

• The net force on the object is directed toward the center of the circular path.

• The direction of the object's velocity is constant.

• The net force on the object is directed away from the center of the circular path.

Multiple Choice

Which has greater angular speed, a horse near the outside rail of a merry-go-round or a horse near the inside rail?

• The inside horse
• The outside horse
• Neither - they both have the same angular speed

Multiple Choice

A bug on a turning phonograph record will make more turns per minute if it is located toward the center of the record.

• True
• False

7.2 Torque and Angular Acceleration

• Torque is the rotational equivalent to a Force. A net torque applied on an object will cause the object to change its rotational motion. 

• If all the torques on an object are balanced (∑𝜏 = 0) then the object is in equilibrium.

Multiple Choice

When solving a torque problem, all lever arms are measured from the

• end of the bar

• pivot or fulcrum

• center of the bar

• center of the mass

Multiple Choice

Does a bridge anchored resting on two pillars have any torque?

• No, it isn't moving

• Yes, but it is at equilibrium

• Yes, but it will soon break because of the torque

• No, Bridges can't have torque

Multiple Choice

A state of equilibrium is also seen below. Each of the cars weighs the same 9800 N. Despite the fact that there is only one car on the left-hand side that is 9 m from the fulcrum, the torques balance because, the cars on the right-hand side, are ____meters from the fulcrum, compared to the car on the left-hand side.

• 4.5 m

• 3 m

• 1 m

• 2 m

Multiple Choice

You apply force to a wrench to tighten a bolt. The wrench breaks in half. Select the best answer for what happens next. Assume the force applied remains constant.

• The torque is now half of what it was, because torque and distance are inversely proportional

• The torque is now half of what it was, because torque and distance are directly proportional

• The torque is now double of what it was, because torque and distance are inversely proportional

• The torque is now double of what it was, because torque and distance are directly proportional

Multiple Choice

Will the torque be increased by using the rope?

• A - Yes
• B - No

Multiple Choice

What is the weight of the package?

• 5 N
• 10 N
• 15 N
• 20 N

Multiple Choice

A seesaw is unbalanced with two people of different masses sitting equal distances from the center. Which of the following will result in equilibrium?

• The larger person moving further away from the center.

• Moving the smaller person closer to the center.

• Moving the smaller person further from the center.

• Making the larger person do nothing.

7.3 Angular Momentum

• L is the angular momentum, I is the moment of inertia of the object, and 𝜔 is the angular velocity of the object.

• A net torque causes a change in the angular momentum of the object.

  
  

Multiple Choice

According to the Law of Conservation of Angular Momentum, if I (momentum of inertia) increases, what will happen to ω?

• Decrease

• Stay the same

• Increase

Multiple Choice

Which of these items is easier to turn?

• Left

• Right

• Both are just as easy to turn

Multiple Choice

What happens to rotational inertia of an object when mass is moved close to axis of rotation?

• Decreases

• Increases

• Stays the Same

Multiple Choice

A skater start spinning on the tips of her skates at low angular velocity with arm outstretched.

What would happen when she brings her arms close to her body

• She will spin slower

• She will spin faster

• She will spin at the same velocity

Multiple Choice

What is happening to the ice skater?

• Decreased Angular velocity, decreased rotational inertia

• Decreased Angular velocity, increased rotational inertia

• Increased Angular velocity, increased rotational inertia

• Increased Angular velocity, decreased rotational inertia