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Worksheet: Newton’s Second Law of Motion for Rotation


A flywheel with a moment of inertia of kg.m2, that has an initial angular velocity of 52.36 rad/s is brought to rest by frictional torque in a time of 120 s. What is the average frictional torque on the flywheel?


A constant torque is applied to a rigid body whose moment of inertia is 4.0 kg⋅m2 around the axis of rotation. If the wheel starts from rest and attains an angular velocity of 20.0 rad/s in 10.0 s, what is the applied torque?


Suppose you exert a force of 180 N tangential to a 0.280-m-radius, 75.0-kg grindstone (a solid disk).

What torque is exerted?

What is the angular acceleration assuming negligible opposing friction?

What is the angular acceleration if there is an opposing frictional force of 20.0 N exerted 1.50 cm from the axis?


A block of mass 3.0 kg slides down an inclined plane at an angle of , as shown. The block is attached to one end of a massless tether. The other end of the tether is attached to a pulley at the top of the incline. The pulley has mass of 1.0 kg, a radius of 0.50 m, and can be approximated as a disk. The coefficient of kinetic friction of the block on the plane is 0.40. What is the magnitude of the acceleration of the block?


An automobile is suspended so that its wheels can turn freely. Each wheel acts like a disk of mass 15.0 kg with a 0.180-m radius. The walls of each tire act like an annular ring of mass 2.00 kg that has inside radius of 0.180 m and outside radius of 0.320 m. The tread of each tire acts like a hoop with a mass of 10.0 kg and a radius 0.330 m. The axle acts like a rod with a 14.0 kg mass that has a 2.00-cm radius. The drive shaft acts like a rod of mass 30.0 kg that has a 3.20-cm radius. The automobile’s engine can produce 200.0 N.m of torque. Calculate the magnitude of the angular acceleration produced by the engine if of this torque is applied to the drive shaft, axle, and rear wheels of a car.


A cord is wrapped around the rim of a solid cylinder of radius 0.25 m, and a constant force of 40 N is exerted on the cord, as shown. The cylinder is mounted on frictionless bearings, and its moment of inertia is 6.0 kg⋅m2.

Calculate the angular velocity of the cylinder after 5.0 m of cord have been removed.

The 40-N applied force is replaced by an object with a weight of 40 N. What is the angular velocity of the cylinder after 5.0 m of cord have unwound?


A flywheel with a moment of inertia kg⋅m2 is accelerated uniformly from rest to an angular velocity of 230 rad/s in 7.00 s by a motor.

What is the angular acceleration of the flywheel?

What is the magnitude of the torque acting on the flywheel?


A torque of 60.0 N⋅m is applied to a grinding wheel with a moment of inertia kg⋅m2 for 60.0 s. The grinding wheel is initially at rest.

What is the angular velocity of the grinding wheel after its acceleration?

What angle does the wheel move through while the torque is applied?


A uniform cylindrical grinding wheel of mass 25.0 kg and diameter 2.00 m is turned by an electric motor. The friction in the wheel’s bearings is negligible. The wheel is accelerated from rest to 120.0 rpm in 20.0 revolutions.

What torque must be applied to the wheel?

A tool whose coefficient of kinetic friction with the wheel is 0.60 is pressed perpendicularly against the wheel with a force of 40.0 N. What torque must be supplied by the motor to keep the wheel rotating at a constant angular velocity?


Zorch, an archenemy of Rotation Man, decides to slow Earth’s rotation to one rotation per 25.0 h by exerting an opposing force at and parallel to the equator. Rotation Man is not immediately concerned, because he knows Zorch can only exert a force of N. For how much time must Zorch push with this force to accomplish his goal? Use a value of kg for the mass of the Earth and a value of m for the Earth’s radius.

  • A year
  • B year
  • C year
  • D year
  • E year


A grindstone can be approximated as a disk. A grindstone has a mass of 75.0 kg, a 0.220-m radius, and is turning at 60.0 rpm. A steel axe is pressed against the grindstone with a radial force of 30.0 N. Use a value of 0.400 for the kinetic coefficient of friction between steel and stone.

Calculate the angular acceleration of the grindstone.

How many rads will the grindstone turn through before coming to rest?