physics.

A flywheel is a solid disk that rotates about an axis that is perpendicular to the disk at its center. Rotating flywheels provide a means for storing energy in the form of rotational kinetic energy and are being considered as a possible alternative to batteries in electric cars. The gasoline burned in a 300-mile trip in a typical midsize car produces about 1.2*10^9 J of energy. How fast would a 13-kg flywheel with a radius of 0.30m have to rotate to store this much energy? Give your answer in rev/min.

I need some hints to do this problem. Please help. Thanks.

  1. 馃憤 0
  2. 馃憥 0
  3. 馃憗 42
asked by Disy
  1. The kinetic energy stored in a rotating object is

    (1/2) I w^2

    I is the moment of inertia of the disk about an axis perpendicular to the disk at the center, which you can look up (If they want you to derive it reply to me that you need a derivation)
    I = (1/2) M R^2 where R is the radius of the flywheel and M is the mass
    w is the angular velocity in radians per second
    w = 2 pi (revolutions per second)
    so set your Joules equal to (1/2) I w^2 and solve for w
    then change w from radians per second to revs per minute
    revs/min = w in rad/sec * 1 rev/2pi radians * 60 seconds/1 minute

    1. 馃憤 0
    2. 馃憥 0
    posted by Damon
  2. I did the same thing, but I can't get the right answer.
    My answer is 4.3*10^5 rev/min

    1. 馃憤 0
    2. 馃憥 0
    posted by Disy
  3. I agree with your answer

    1. 馃憤 0
    2. 馃憥 0
    posted by Damon
  4. But the book says the right answer should be 6.0*10^5rev/min

    1. 馃憤 0
    2. 馃憥 0
    posted by Disy
  5. That is pretty mysterious.

    1. 馃憤 0
    2. 馃憥 0
    posted by Damon

Respond to this Question

First Name

Your Response

Similar Questions

  1. Physics

    A flywheel is a solid disk that rotates about an axis that is perpendicular to the disk at its center. Rotating flywheels provide a means for storing energy in the form of rotational kinetic energy and are being considered as a

    asked by StressedStudent on November 3, 2012
  2. physics

    A flywheel is a solid disk that rotates about an axis that is perpendicular to the disk at its center. Rotating flywheels provide a means for storing energy in the form of rotational kinetic energy and are being considered as a

    asked by reghuir on April 5, 2016
  3. physics

    A solid disk rotates in the horizontal plane at an angular velocity of 0.040 rad/s with respect to an axis perpendicular to the disk at its center. The moment of inertia of the disk is 0.13 kg路m2. From above, sand is dropped

    asked by bob on November 16, 2014
  4. Physics

    A solid disk rotates in the horizontal plane at an angular velocity of 0.034 rad/s with respect to an axis perpendicular to the disk at its center. The moment of inertia of the disk is 0.11 kg路m2. From above, sand is dropped

    asked by Kristi on August 16, 2011
  5. Physics

    A solid disk rotates in the horizontal plane at an angular velocity of 0.036 rad/s with respect to an axis perpendicular to the disk at its center. The moment of inertia of the disk is 0.17 kg 路 m2. From above, sand is dropped

    asked by jason on November 1, 2011
  6. Physics

    A solid disk rotates in the horizontal plane at an angular velocity of 0.0653 rad/s with respect to an axis perpendicular to the disk at its center. The moment of inertia of the disk is 0.156 kg路m2. From above, sand is dropped

    asked by Physic on February 23, 2016
  7. Physics

    A solid disk rotates in the horizontal plane at an angular velocity of 0.0684 rad/s with respect to an axis perpendicular to the disk at its center. The moment of inertia of the disk is 0.190 kg路m2. From above, sand is dropped

    asked by Anna on March 3, 2016
  8. Physics

    The flywheel of an old steam engine is a solid homogeneous metal disk of mass M = 120 kg and radius R = 80 cm. The engine rotates the wheel at 500 rpm. In an emergency, to bring the engine to a stop, the flywheel is disengaged

    asked by Temi on October 18, 2011
  9. Hard Physics Problem

    The flywheel of an old steam engine is a solid homogeneous metal disk of mass M = 131 kgand radius R = 80 cm.The engine rotates the wheel at 580 rpm. In an emergency, to bring the engine to a stop, the flywheel is disengaged from

    asked by Donny on October 25, 2010
  10. Physics

    The flywheel of an old steam engine is a solid homogeneous metal disk of mass M = 114 kgand radius R = 80 cm.The engine rotates the wheel at 540 rpm. In an emergency, to bring the engine to a stop, the flywheel is disengaged from

    asked by Donny on October 24, 2010

More Similar Questions