Exam 9: Rotational Dynamics

9-3 A 2.0-kg hoop rolls without slipping on a horizontal surface so that its center proceeds to the right with a constant linear speed of 6.0 m/s. -Which one of the following statements is true concerning the angular momentum of this hoop?

A uniform disk of radius 1.2 m and mass 0.60 kg is rotating at 25 rad/s around an axis that passes through its center and is perpendicular to the disk.A rod makes contact with the rotating disk with a force of 4.5 N at a point 0.75 m from the axis of rotation as shown.The disk is brought to a stop in 5.0 s.What is the coefficient of kinetic friction for the two materials in contact?

A uniform 13-kg trap door is oriented horizontally and hinged as shown.What is the magnitude of the torque on the door at the instant that the release is activated and the door can freely rotate?

A solid cylinder with a mass m and radius r is mounted so that it can be rotated about an axis that passes through the center of both ends.At what angular speed $\omega$ must the cylinder rotate to have the same total kinetic energy that it would have if it were moving horizontally with a speed v without rotation?

A solid sphere of radius R rotates about a diameter with an angular speed $\omega$ .The sphere then collapses under the action of internal forces to a final radius R/2.What is the final angular speed of the sphere?

Consider four point masses located as shown in the sketch.The acceleration due to gravity is the same everywhere.What is the x coordinate of the center of gravity for this system?

An 80-kg man balances the boy on a teeter-totter as shown.Note: Ignore the weight of the board. -What, approximately, is the magnitude of the downward force exerted on the fulcrum?

A 1.0-kg wheel in the form of a solid disk rolls along a horizontal surface with a speed of 6.0 m/s.What is the total kinetic energy of the wheel?

A certain merry-go-round is accelerated uniformly from rest and attains an angular speed of 1.2 rad/s in the first 18 seconds.If the net applied torque is 1200 N . m, what is the moment of inertia of the merry-go-round?

9-3 A 2.0-kg hoop rolls without slipping on a horizontal surface so that its center proceeds to the right with a constant linear speed of 6.0 m/s. -What is the total kinetic energy of the hoop?

A 14-kg beam is hinged at one end.A 6.0-kg triangular object and a 7.5-kg I-shaped object are positioned as shown.Dots indicate the individual centers of gravity of the beam and the two objects.What is the distance from the axis of rotation to the center of gravity for this system?

The drawing shows the top view of a door that is 1.68 m wide.Two forces are applied to the door as indicated.What is the magnitude of the net torque on the door with respect to the hinge?

A hollow sphere of radius 0.25 m is rotating at 13 rad/s about an axis that passes through its center.The mass of the sphere is 3.8 kg.Assuming a constant net torque is applied to the sphere, how much work is required to bring the sphere to a stop?

Complete the following statement: A body is in translational equilibrium

A string is tied to a doorknob 0.72 m from the hinge as illustrated in the figure.At the instant shown, the force applied to the string is 5.0 N.What is the magnitude of the torque on the door?

Three children are pulling on a rotatable platform on a playground.The platform has a radius of 3.80 m.In the picture, two children are pulling with equal forces of 40.0 N in an attempt to make the platform rotate clockwise.The third child applies a force of 60 N as shown.What is the net torque on the platform? Note: "ccw" is counterclockwise and "cw" is clockwise.

Consider the following three objects, each of the same mass and radius: All three are released from rest at the top of an inclined plane.The three objects proceed down the incline undergoing rolling motion without slipping.In which order do the objects reach the bottom of the incline?