**AP Physics 1 Question 132: Answer and Explanation**

### Test Information

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**Question: 132**

**2.**

A rigid rod is pivoted at its right end. Three forces of identical magnitude but different directions are applied at the positions 1, 2, and 3 as shown. Which of the following correctly ranks the torques *τ*_{1}, *τ*_{2}, and *τ*_{3} provided by the forces *F*_{1}, *F*_{2}, and *F*_{3}?

- A.
*τ*_{1}>*τ*_{2}>*τ*_{3} - B.
*τ*_{3}>*τ*_{2}>*τ*_{1} - C.
*τ*_{2}>*τ*_{1}>*τ*_{3} - D.
*τ*_{2}>*τ*_{1}=*τ*_{3}

**Correct Answer:** A

**Explanation:**

**A**-Torque is force times distance from a fulcrum; but that force must be perpendicular to the rod, so in this case the force used in the equation will be the vertical component, which includes a sin 45^{o} term for *F*_{1} and *F*_{3}. The sine of 45^{o} is 0.7; call the length of the rod *L*, so *F*_{2} is a distance *L*/2 from the pivot, and *F*_{3} is about *L*/4 from the pivot. So *τ*_{1} = 0.7*FL. τ*_{2} = 0.5*FL. τ*_{3} = (0.7·0.25)*FL*.