Question

Which of the following are means of maximizing the torque of a force applied to a rotating object?
I. Maximize the magnitude of the applied force.
II. Apply the force as close as possible to the axis of rotation.
III. Apply the force perpendicular to the displacement vector between the axis of rotation and the point of applied force.

• A. I only
• B. II only
• C. I and II only
• D. I and III only
• E. I, II and III

Answer 1

Answer: (D)

I and III only

The torque on an object is given by the formula $\tau =r\times F$ where $F$ is the applied force and $r$ is the distance of the applied force from the axis of rotation. In order to maximize this cross product, we need to maximize the two quantities and insure that they are perpendicular to one another. Statement I maximizes F and statement III demands that F and r be perpendicular, but statement II minimizes r rather than maximizing it, so statement II is false.