Page 7 - Solutions Manual to accompany Electric Machinery Fundamentals

Chapter 1: Introduction to Machinery Principles

1-1. A motor’s shaft is spinning at a speed of 1800 r/min. What is the shaft speed in radians per second?
SOLUTION The speed in radians per second is

   1800 r/min   1 min     2 rad     188.5 rad/s
 60 s   1 r 
2
1-2. A flywheel with a moment of inertia of 4 kg  m is initially at rest. If a torque of 6 N  m
(counterclockwise) is suddenly applied to the flywheel, what will be the speed of the flywheel after 5 s?
Express that speed in both radians per second and revolutions per minute.

SOLUTION The speed in radians per second is:

   6 N m
 t    t   5  s  7.5 rad/s


 J  4 kg m 2
The speed in revolutions per minute is:
n   7.5 rad/s   1 r     60 s    71.6 r/min
 2 rad    1 min 
1-3. A force of 10 N is applied to a cylinder, as shown in Figure P1-1. What are the magnitude and direction
of the torque produced on the cylinder? What is the angular acceleration  of the cylinder?

SOLUTION The magnitude and the direction of the torque on this cylinder is:
 ind  rF sin , CCW
 ind  0.15 m 10 N sin 30   0.75 N m, CCW

The resulting angular acceleration is:

 0.75 N m

    0.188 rad/s
2

J 4 kg m 2
1-4. A motor is supplying 50 N  m of torque to its load. If the motor’s shaft is turning at 1500 r/min, what is
the mechanical power supplied to the load in watts? In horsepower?
SOLUTION The mechanical power supplied to the load is

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