Question

an airplanes propeller completes one revolution in 65ms. a)what is the angular speed in rpm? in rad/s?

Answer 1

-- We already know the rate of revolutions per time ...
it's 1 revolution per 0.065 sec.  We just have to
unit-convert that to 'per minute'.

(1 rev / 0.065 sec) x (60 sec / min) = (1 x 60) / (0.065) = 923 RPM  (rounded)
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-- 1 revolution = 2π radians

  (2π rad) / (0.065 sec) = (2π / 0.065) = 96.66 rad/sec  (rounded)