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Ch 10: Dynamics of Rotational Motion
Young & Freedman Calc - University Physics 15th Edition
Young & Freedman Calc15th EditionUniversity PhysicsISBN: 9780135159552Not the one you use?Change textbook
Chapter 10, Problem 7b

A machinist is using a wrench to loosen a nut. The wrench is 25.0 cm long, and he exerts a 17.0-N force at the end of the handle at 37° with the handle (Fig. E10.7). What is the maximum torque he could exert with this force, and how should the force be oriented?
A wrench applying a 17.0 N force at 37° to loosen a nut, 25.0 cm long.

Verified step by step guidance
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Understand that torque (τ) is calculated using the formula: τ = r * F * sin(θ), where r is the length of the wrench, F is the force applied, and θ is the angle between the force and the lever arm.
Convert the length of the wrench from centimeters to meters to maintain SI units. Since 1 cm = 0.01 m, 25.0 cm = 0.25 m.
Identify the given values: r = 0.25 m, F = 17.0 N, and θ = 37°.
Calculate the torque using the formula τ = r * F * sin(θ). Substitute the known values into the equation: τ = 0.25 m * 17.0 N * sin(37°).
To exert the maximum torque, the force should be applied perpendicular to the wrench. This means the angle θ should be 90°, making sin(θ) = 1. Therefore, the maximum torque is τ_max = r * F when θ = 90°.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Torque

Torque is a measure of the rotational force applied to an object, calculated as the product of the force and the distance from the pivot point (lever arm) at which the force is applied. It is given by the formula τ = r × F × sin(θ), where τ is torque, r is the length of the lever arm, F is the force applied, and θ is the angle between the force vector and the lever arm. Understanding torque is essential for determining how effectively a force can cause an object to rotate.
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Lever Arm

The lever arm is the perpendicular distance from the axis of rotation to the line of action of the force. In the context of a wrench, the lever arm is the length of the wrench itself, which in this case is 25.0 cm. The longer the lever arm, the greater the torque produced for the same amount of force, making it crucial to maximize this distance when applying force to loosen or tighten nuts.
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Angle of Application

The angle at which a force is applied significantly affects the torque generated. The maximum torque occurs when the force is applied perpendicular to the lever arm (θ = 90°), resulting in sin(θ) = 1. In this scenario, the force is applied at an angle of 37°, which means that the effective component of the force contributing to torque is reduced. Understanding how to orient the force for maximum torque is key to effectively using tools like a wrench.
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Related Practice
Textbook Question

Three forces are applied to a wheel of radius 0.350 m, as shown in Fig. E10.4. One force is perpendicular to the rim, one is tangent to it, and the other one makes a 40.0° angle with the radius. What is the net torque on the wheel due to these three forces for an axis perpendicular to the wheel and passing through its center?

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Textbook Question

A metal bar is in the xyxy-plane with one end of the bar at the origin. A force F=(7.00N)i+(3.00N)j\(\overrightarrow{F}\)=\(\left\)(7.00N\(\right\))i+(-3.00N)j is applied to the bar at the point x=3.00 mx=3.00\(\text{ m}\), y=4.00 my=4.00\(\text{ m}\). What are the magnitude and direction of the torque with respect to the origin produced by F\(\overrightarrow{F}\)?

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Textbook Question

The flywheel of an engine has moment of inertia 1.60 kg/m2 about its rotation axis. What constant torque is required to bring it up to an angular speed of 400 rev/min in 8.00 s, starting from rest?

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Textbook Question

(a) Calculate the magnitude of the angular momentum of the earth in a circular orbit around the sun. Is it reasonable to model it as a particle? Consult Appendix E and the astronomical data in Appendix F

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Textbook Question

A machinist is using a wrench to loosen a nut. The wrench is 25.0 cm long, and he exerts a 17.0-N force at the end of the handle at 37° with the handle (Fig. E10.7). What torque does the machinist exert about the center of the nut?

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Textbook Question

A metal bar is in the xyxy-plane with one end of the bar at the origin. A force F=(7.00N)i+(3.00N)j\(\overrightarrow{F}\)=\(\left\)(7.00N\(\right\))i+(-3.00N)j is applied to the bar at the point x=3.00 mx=3.00\(\text{ m}\), y=4.00 my=4.00\(\text{ m}\). In terms of unit vectors ii and jj, what is the position vector rr for the point where the force is applied?

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