# physics

posted by .

A flywheel of moment of inertia 0.32 kgm^2 is rotated steadily at 120rad/s by a 50 W electric motor. (i)find the kinetic energy and angular momentum of the flywheel. (ii) calculate the value of frictional couple opposing the rotation. (iii)find the time taken for the wheel to come to rest after the motor has been switched off.

• physics -

(i) First compute the moment of inertia, I, with the formula for a disc or cyliner. The kinetic energy is (1/2)I w^2 and the angular momentum is I w.

(ii) The electric power driving the motion is T*w, where T is the torque. Set that equal to the 50W electrical power input and solve for T. The electrical motor torque in steady state operation equals the frictional torque. The words torque and couple are interchangeable.

(iii) During the slowdown time, t:

T*t = initial angular momentum = I w.

You know T from (ii) and I w from (i). . Solve for the time, t.

## Similar Questions

1. ### physic

hi,need help please.thank. A car is designed to get its energy from a rotating flywheel (solid disk) with a radius of 2.00 m and a mass of 525 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's …
2. ### Physics Rotaional Kinetic Energy

A car is designed to get its energy from a rotating flywheel with a radius of 1.50 m and a mass of 600 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 4000 rev/min. …
3. ### physics

In the design of a passenger bus, it is proposed to derive the motive power from the energy stored in a flywheel. The flywheel, which has a moment of inertia of 4.0 x 10^2 kgm^2, is accelerated to its maximum rate of rotation 3.0 x …
4. ### kinetics

An exercise bicycle's flywheel is 30cm in diameter and 2.5 cm thick and is constructed from steel (density=7850 kg m3) its moment of inertia is 0.156 kg m2 about its axis of rotation a) calculate the mass of the flywheel b) calculate …
5. ### kinetics

An exercise bicycle's flywheel is 30cm in diameter and 2.5 cm thick and is constructed from steel (density=7850 kg m3) its moment of inertia is 0.156 kg m2 about its axis of rotation a) calculate the mass of the flywheel b) calculate …
6. ### kinetics

An exercise bicycle's flywheel is 30cm in diameter and 2.5 cm thick and is constructed from steel (density=7850 kg m3) its moment of inertia is 0.156 kg m2 about its axis of rotation a) calculate the mass of the flywheel b) calculate …
7. ### kinetics

An exercise bicycle's flywheel is 30cm in diameter and 2.5 cm thick and is constructed from steel (density=7850 kg m3) its moment of inertia is 0.156 kg m2 about its axis of rotation a) calculate the mass of the flywheel b) calculate …
8. ### engineering mechanics

An exercise bicycle's flywheel is 30cm in diameter and 2.5 cm thick and is constructed from steel (density=7850 kg m3) its moment of inertia is 0.156 kg m2 about its axis of rotation a) calculate the mass of the flywheel b) calculate …
9. ### engineering mechanics

An exercise bicycle's flywheel is 30cm in diameter and 2.5 cm thick and is constructed from steel (density=7850 kg m3) its moment of inertia is 0.156 kg m2 about its axis of rotation a) calculate the mass of the flywheel b) calculate …
10. ### kinematics

An exercise bicycle's flywheel is 30cm in diameter and 2.5 cm thick and is constructed from steel (density=7850 kg m3) its moment of inertia is 0.156 kg m2 about its axis of rotation a) calculate the mass of the flywheel b) calculate …

More Similar Questions