Simple Statics problem I am having brain fart on

  • Thread starter Thread starter wkfrst
  • Start date Start date
  • Tags Tags
    Brain Statics
Click For Summary

Discussion Overview

The discussion revolves around a statics problem involving the calculation of normal forces on a car's tires when the vehicle is in equilibrium. Participants explore the setup of the problem, the equations applicable to static analysis, and the implications of the car's center of gravity on the calculations.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant describes the problem setup, including the mass of the car and the location of the center of gravity relative to the front tire.
  • The participant outlines the equations used for static problems, specifically mentioning the sum of forces in the x and y directions and the sum of moments about a point.
  • Another participant questions the clarity of the center of gravity's position, pointing out a potential discrepancy in the measurements provided.
  • A later reply notes that the initial calculation assumed the car had only two tires, which led to an incorrect factor in the normal force calculation, suggesting that the normal force should be shared among four tires instead.
  • One participant expresses realization of a mistake after receiving feedback, acknowledging the error in their initial approach.

Areas of Agreement / Disagreement

Participants generally agree on the need to clarify the center of gravity's position and the implications of the number of tires on the normal force calculation. However, the discussion does not reach a consensus on the correct final answer, as the initial calculations remain disputed.

Contextual Notes

There is uncertainty regarding the exact position of the center of gravity and how it affects the calculations. Additionally, the initial assumption of the number of tires is a critical factor that has not been fully resolved.

wkfrst
Messages
4
Reaction score
0
I know I am missing something simple here. This is only the second problem and I have done the rest with no problems. I would appreciate a second set of eyes.

Homework Statement



The mass center G of the 1430-kg rear-engine car is located as shown in the figure. Determine the normal force under the left front tire (a)Nf (point F) and under the left rear tire (b)Nr (point R) when the car is in equilibrium.

F is the front tire. Center of gravity is 1406mm to the right of F. R is rear tire which is 972mm from CG or 2378 to the right of F.

Homework Equations



I know you can use 3 different equations to solve these 2D static problems. Sum of forces in x direction, sum of forces in y direction, and sum of the moment about a point of your choosing.

The Attempt at a Solution


All the forces are normal to the x-axis so there are no forces acting in the x direction. Summing in the y-direction gives you two unknowns of F(front) and R(rear).
I chose to sum the moment about F. The normal force at F slides through the point so the it's contribution is zero.

M about F= (9.81m/s^2)(1430kg)(1.406m)-R(2.378m)=0
I chose clockwise to be positive.
The answer I get for R is 8294N but apparently is wrong. I am guessing I am over looking something simple.
Thanks for the help!
 
Last edited:
Physics news on Phys.org
First clarify the CG...is it 1423 or 1406 mmm to the right of F?

Your equation otherwise would appear correct, except that most cars have 4 tires, not 2. :wink:
 
woops sorry. The CG is 1406mm to the right of the front tire.
Interesting side note. I found an similar example with an answer and was able to find out that my answer was double the correct answer. Now I am even more confused:)
 
wkfrst said:
woops sorry. The CG is 1406mm to the right of the front tire.
Interesting side note. I found an similar example with an answer and was able to find out that my answer was double the correct answer. Now I am even more confused:)

your answer assumed that the car had 2 tires..one front and one back...but the car has 4 tires, 2 front and 2 back, so the normal force you calculated is shared by 2 tires...that's why your answer is off by a factor of 2...
 
Wow thanks. I knew it was a brilliant mistake somewhere.
 

Similar threads

Engineering Statics, Finding Reaction forces for A and H
  • · Replies 6 ·
Replies
6
Views
2K
Engineering Solving a Moment Vector Direction Problem: An Example from Statics Textbook
  • · Replies 2 ·
Replies
2
Views
2K
Engineering Instantaneous Center of Rotation (Polplan in german) and STATICS
  • · Replies 1 ·
Replies
1
Views
2K
Engineering Moment of a force about point O
  • · Replies 4 ·
Replies
4
Views
3K
Determine the vertical reaction force
  • · Replies 11 ·
Replies
11
Views
4K
Equivalent force and couple moment
  • · Replies 2 ·
Replies
2
Views
2K
Mastering 3D Statics: How to Solve Moments and Forces for Bearings A and B
  • · Replies 1 ·
Replies
1
Views
3K
Direction of static friction between a vehicle and circular dome
  • · Replies 9 ·
Replies
9
Views
2K
Statics: 3D Equilibrium Problem r X F or Fd?
  • · Replies 3 ·
Replies
3
Views
5K
What am I doing wrong on this Statics Problem?
  • · Replies 1 ·
Replies
1
Views
1K