## Q. 8.1

## Chapter 8

## Q. 8.1

**BATTLE OF THE REVOLVING DOOR**

**GOAL** Apply the basic definition of torque.

**PROBLEM** Two disgruntled businesspeople are trying to use a revolving door, which is initially at rest (see Fig. 8.3.) The woman on the left exerts a force of 625 \mathrm{~N} perpendicular to the door and 1.20 \mathrm{~m} from the hub’s center, while the man on the right exerts a force of 8.50 \times 10^{2} \mathrm{~N} perpendicular to the door and 0.800 \mathrm{~m} from the hub’s center. Find the net torque on the revolving door.

**STRATEGY** Calculate the individual torques on the door using the definition of torque, Equation 8.1,

\tau = rF [8.1]

and then sum to find the net torque on the door. The woman exerts a negative torque, the man a positive torque. Their positions of application also differ.

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