Work and Power in Rotational Motion

Ms. Mikaela Fudolig

Physics 71 Lecture

Work done by a torque

Suppose that the torque is along the z-axis, and that the object on which the torque is applied rotates by = f - i. The work done by the torque on the object is

f

i

zW d

Work done by a torque

Suppose that the torque is along the z-axis, and that the object on which the torque is applied rotates by = f - i. The work done by the torque on the object is

zW CONSTANT TORQUE

Work done by a torque

Usually, the work done by an external torque is considered as part of “Wothers” in the work-energy theorem.

Power

The power associated with the work done by a torque acting on a rotating object is

dWP

dt

Power

If the torque is constant over time:

z

dP

dt

Power

And we can express the power as

zP

Example 1

A 1.50-kg grinding wheel is in the form of a solid cylinder of radius 0.100m. What constant torque will bring it from rest to an angular speed of 1200rev/min in 2.5s?

Example 2

What is the power output of an electric motor turning at 4800 rev/min and developing a torque of 480Nm?