A flywheel rotates at 7200 rpm when the power is suddenly cut off. The flywheel decelerates at a constant rate of 2.1 rad/s2 and comes to rest 5 min later. How many revolutions does the flywheel make before coming to rest?

20960.7 revolutions

Explanation:

Convert from revolutions-per-minute to angular speed (rad/s) knowing that each revolution has a 2π angle and each minute has 60 seconds

7200 rpm = 7200 (rev/min) * 2π (rad/rev) * (1/60) (min/sec) = 754 rad/s

We can use the following equation of motion to calculate the angle swept by the flywheel during the deceleration of t = 5 minute = 300 s

Again we can convert this to number of revolution

131700 rad * (1/2π) (rev/rad) = 20960.7 rev

0.3x0.21x0.08kg=mass 1 sheet

mass 500 = 500xmass 1

volume pile = 0.3x0.2x0.048

density=mass/volume= 500xmass 1/0.3x0.2x0.048

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