What is the torque exerted by a stationary car on its rear wheels?

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Homework Help Overview

The problem involves calculating the torque exerted by a stationary car on its rear wheels, given specific dimensions and mass of the car, as well as the angle at which it is jacked up. The context is rooted in mechanics, particularly focusing on torque and forces acting on a body in equilibrium.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the importance of identifying the pivot point and the role of the center of mass in calculating torque. Questions arise regarding the correct interpretation of the problem and the necessary adjustments for the angle of the car.

Discussion Status

The discussion is ongoing, with some participants offering guidance on how to approach the problem, particularly regarding the calculation of distances and the effects of the angle. There is an acknowledgment of initial confusion, but progress is being made as participants clarify their understanding.

Contextual Notes

Participants note the need to consider the angle of the car and the position of the center of mass relative to the pivot point when calculating torque. There is also mention of potential issues with calculator settings affecting the calculations.

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Homework Statement


A mechanic jacks up a car to an angle of 10.0° to change the front tires. The car is 2.95 m long and has a mass of 1150 kg. Its center of mass is located 1.12 m from the front end. The rear wheels are 0.40 m from the back end. Calculate the torque exerted by the car around the back wheels.


Homework Equations


T = F x r x sintheta
sum of the torques = 0
F = ma


The Attempt at a Solution


Clueless when I have to figure out where the gravity is acting, and so forth. Basically, I don't know where to start.
 
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Welcome to PF.

Start by drawing a diagram.

You are going to use the back wheel at the pivot point. And the sum of the Torques are going to be 0.

But the question only looks like it wants the torque from the car, not the jack. So ... how far is the center of mass from the pivot along the horizontal after taking into account the angle the car is tilted at?

That's about all you need to answer it.
 
So you subtract the lengths to get from the jack to the rear wheels?
 
Okay. I think I got it...part of my problem was that I didn't have my calculator set in degrees. The other part of my problem was that I had originally gotten the torque from the jack, not from the car.

Thank you for your help!
 

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