While spinning down from 500.0 rpm to rest, a solid uniform flywheel (disk) does 2.3 kj of work. if the radius of the disk is 1.2 m, what is its mass? a) 3.0 kg b) 2.3 kg c) 2.6 kg d) 2.0 kg

Option (B)

Explanation:

Let m be the mass of solid disc.

initial frequency, fo = 500 rpm = 8.33 rps

initial angular velocity, ωo = 2 x 3.14 x 8.33 = 52.33 rad/s

final angular velocity, ω = 0 rad/s

Work done = change in kinetic energy

Let I be the moment of inertia of the disc

Initial kinetic energy

K1 = 1369.2 I

Final kinetic energy

K2 = 0

Change in Kinetic energy = 1369.2 I

So, Work done

2.3 x 1000 = 1369.2 x 0.72 m

2300 = 985.82 m

m = 2.3 kg

Option (B)

the answer is 46 mls because when you add the speed per second it increses the speed

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.