Exam 12: Torque

A solid uniform sphere of mass 1.85 kg and diameter 45.0 cm spins about an axle through its center.Starting with an angular velocity of 2.40 rev/s,it stops after turning through 18.2 rev with uniform acceleration.The net torque acting on this sphere as it is slowing down is closest to

A ball is released from rest on a no-slip surface,as shown in the figure.After reaching its lowest point,the ball begins to rise again,this time on a frictionless surface as shown in the figure.When the ball reaches its maximum height on the frictionless surface,it is

A 120-kg refrigerator,2.00 m tall and 85.0 cm wide,has its center of mass at its geometrical center.You are attempting to slide it along the floor by pushing horizontally on the side of the refrigerator.The coefficient of static friction between the floor and the refrigerator is 0.300.Depending on where you push,the refrigerator may start to tip over before it starts to slide along the floor.What is the highest distance above the floor that you can push the refrigerator so that it won't tip before it begins to slide?

If two vectors are perpendicular to each other,their cross product must be zero.

A solid sphere,solid cylinder,and a hollow pipe all have equal masses and radii and are of uniform density.If the three are released simultaneously at the top of an inclined plane and roll without slipping,which one will reach the bottom first?

A uniform solid cylinder of radius R and a thin uniform spherical shell of radius R both roll without slipping. If both objects have the same mass and the same kinetic energy,what is the ratio of the linear speed of the cylinder to the linear speed of the spherical shell?

In the figure,a uniform rectangular crate 0.40 m wide and 1.0 m tall rests on a horizontal surface.The crate weighs 930 N,and its center of gravity is at its geometric center.A horizontal force F is applied at a distance h above the floor.If h = 0.61 m,what minimum value of F is required to make the crate start to tip over? Static friction is large enough that the crate does not start to slide.

In the figure,the horizontal lower arm has a mass of 2.8 kg and its center of gravity is 12 cm from the elbow joint pivot.How much force F_M must the vertical extensor muscle in the upper arm exert on the lower arm to hold a 7.5 kg shot put?

A 20.0-kg uniform door has a width of 1.20 m and a height of 2.50 m.The door is mounted on a post by a pair of hinges,marked 1 and 2 in the figure,at the top and bottom of the door.An external force of 60.0 N,at an angle of 30.0° above the horizontal,is applied to the small doorknob,as shown in the figure.The doorknob is 1.00 m above the bottom of the door. (a)Find the x component of the force that hinge 1 exerts on the door at the top. (b)Find the SUM of the y components of the forces that hinges 1 and 2 together exert on the door.

A nonuniform,80.0-g,meterstick balances when the support is placed at the 51.0-cm mark.At what location on the meterstick should a 5.00-g tack be placed so that the stick will balance at the 50.0 cm mark?

If two vectors point in opposite directions,their cross product must be zero.

When you ride a bicycle,in what direction is the angular velocity of the wheels?

A uniform solid sphere of mass 1.5 kg and diameter 30.0 cm starts from rest and rolls without slipping down a 35° incline that is 7.0 m long. (a)Calculate the linear speed of the center of the sphere when it reaches the bottom of the incline. (b)Determine the angular speed of the sphere about its center at the bottom of the incline. (c)Through what angle (in radians)does this sphere turn as it rolls down the incline? (d)Does the linear speed in (a)depend on the radius or mass of the sphere? Does the angular speed in (b)depend on the radius or mass of the sphere?

A tire is rolling along a road,without slipping,with a velocity v.A piece of tape is attached to the tire.When the tape is opposite the road (at the top of the tire),its velocity with respect to the road is

A 5.0-m long,12-kg uniform ladder rests against a smooth vertical wall with the bottom of the ladder 3.0 m from the wall.The coefficient of static friction between the floor and the ladder is 0.28.What distance,measured along the ladder from the bottom,can a 60-kg person climb before the ladder starts to slip?

A solid,uniform sphere of mass 2.0 kg and radius 1.7 m rolls from rest without slipping down an inclined plane of height 7.0 m.What is the angular velocity of the sphere at the bottom of the inclined plane?

As you are leaving a building,the door opens outward.If the hinges on the door are on your right,what is the direction of the angular velocity of the door as you open it?

The angular momentum of a system remains constant

In an experiment,a student brings up the rotational speed of a piece of laboratory apparatus to 30.0 rpm.She then allows the apparatus to slow down uniformly on its own,and counts 240 revolutions before the apparatus comes to a stop.The moment of inertia of the apparatus is known to be 0.0850 kg•m².What is the magnitude of the retarding torque on the apparatus?

If = -2 - 6 + 2 And = -2 -2 - 3 ,which of the following numbers is closest to the magnitude of × ?