4. Cooks often pulse food in a food processor by repeatedly turning the power to

Question

4. Cooks often pulse food in a food processor by repeatedly turning the power to the motor on and off. The blade has mass 50 g and a diameter of 12 cm and gets up to an angular speed of 200 rpm before the power is shut off. The power is kept off for 1.0 s, and during this time the blade slows due to revolutions A. (10 Pts) At what rate is the blade spinning when the power comes back on? friction in its axle bearings. During the time the power is off,the blade makes 2 complete (10 Pts) How many revolutions would the blade make if the power was shut off and not turned back on? B.

Explanation / Answer

A] Using second equation of rotation,

s = ut + 0.5at^2

2 = (200/60)*1 + 0.5*1^2 a

a = [2 - 200/60]/0.5 = -2.6667 rev/s^2

v = u+at = 200/60 -2.6667*1 = 0.6667 rev/s

v = 0.6667*60 rpm

= 40 rpm answer

B] Using third of rotation, s = [v^2-u^2]/2a

= [0 - (200/60)^2]/[2*-2.6667]

= 2.083 revolutions

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