Simple Statics problem I am having brain fart on

In summary, the question is about determining the normal forces at two points on a rear-engine car in equilibrium. The mass center of the car is shown in a figure and the equations needed to solve the problem are given. The attempt at a solution involves summing forces in the y-direction and moments about a chosen point, with the front tire having no contribution to the moment. The mistake in the calculation is that the car has 4 tires instead of 2, resulting in the normal forces being shared by 2 tires and the calculated answer being off by a factor of 2.
  • #1
wkfrst
4
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
  • #2
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:
 
  • #3
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:)
 
  • #4
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...
 
  • #5
Wow thanks. I knew it was a brilliant mistake somewhere.
 

Related to Simple Statics problem I am having brain fart on

1. What is statics and why is it important?

Statics is a branch of mechanics that studies the behavior of stationary objects under the influence of forces. It is important because it helps us understand and analyze the forces acting on structures and objects, and how these forces affect their equilibrium and stability.

2. What is a "simple statics problem"?

A simple statics problem involves analyzing the forces acting on a stationary object or structure in order to determine the equilibrium and stability of the system. It typically involves finding the resultant force, moment, or center of gravity of the system.

3. What are the common challenges in solving a simple statics problem?

The most common challenges in solving a simple statics problem include identifying all the forces acting on the system, understanding the concept of equilibrium, and correctly applying the equations of statics to the problem.

4. How can I improve my problem-solving skills in statics?

To improve your problem-solving skills in statics, it is important to practice solving different types of problems and familiarize yourself with the fundamental principles and equations of statics. You can also seek help from a tutor or join a study group to gain a better understanding of the subject.

5. What are some real-life applications of statics?

Statics has a wide range of real-life applications, including analyzing the forces acting on buildings, bridges, and other structures, designing machinery and mechanical systems, and understanding the stability of objects and structures in various situations such as earthquakes and wind loads.

Similar threads

Engineering Solving a Moment Vector Direction Problem: An Example from Statics Textbook
    • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
Engineering Moment of a force about point O
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
Direction of static friction between a vehicle and circular dome
    • Introductory Physics Homework Help
Replies
9
Views
1K
Determine the vertical reaction force
    • Engineering and Comp Sci Homework Help
Replies
11
Views
3K
Engineering Struggling with a Structural Analysis Problem?
    • Engineering and Comp Sci Homework Help
Replies
1
Views
917
Equivalent force and couple moment
    • Engineering and Comp Sci Homework Help
Replies
2
Views
2K
Why Is Taking Moments at Point A' Incorrect in Rotational Balance Problems?
    • Introductory Physics Homework Help
Replies
14
Views
1K
Mastering 3D Statics: How to Solve Moments and Forces for Bearings A and B
    • Engineering and Comp Sci Homework Help
Replies
1
Views
2K
I Statics: When the reactions depend on the displacements
    • Mechanics
Replies
5
Views
910
How to interpret the center of aero forces on a sports car?
    • Introductory Physics Homework Help
Replies
25
Views
1K

Hot Threads

Recent Insights

Back
Top