A pottery wheel primarily consists of a motor and a heavy platter to turn the cl

Question

A pottery wheel primarily consists of a motor and a heavy platter to turn the clay while it is molded. The motor is rated at 0.5 hp. The maximum speed of 270 rpm can be reached in 2.9 seconds. The mass and diameter of the disc are 40 kg and 60 cm respectively. Determine: a. the amount of work done by the motor including frictional energy losses. [1081.7 J] b. the net torque while motor is on. [17.55 Nm] c. the amount of the friction torque needed to stop the wheel in 5 s after the motor is turned off. [10.18 N m]

Explanation / Answer

3. (A) Power = 0.5 hp = 0.5 x 746 = 373 Watt

Energy = Power x time

= 373 x 2.9

= 1081.7 J

So work done = 1081.7 J

(B) w = 270 rpm = 270 x 2pi rad / 60 s

w = 28.27 rad/s

Applying wf = wi + alpha t

28.27 = 0 + 2.9 alpha

alpha = 9.75 rad/s^2

I = 40 x 0.30^2 /2 = 1.8 kg m^2

Net torque = I alpha = 17.55 N m

(C) now wi = 28.27 rad/s

wf = 0

0 = 28.28 - alpha (5)

alpha = 5.65 rad/s^2

torque = 1.8 x 5.65 =10.18 N m

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