Solving Mechanics Friction Problem: How to Calculate Contact Force

  • Context: MHB 
  • Thread starter Thread starter Shah 72
  • Start date Start date
  • Tags Tags
    Friction Mechanics
Click For Summary

Discussion Overview

The discussion revolves around solving a mechanics problem involving friction and contact forces on an incline. Participants are attempting to calculate the contact force and coefficient of friction based on a given scenario, with a focus on free body diagrams (FBD) and static equilibrium conditions.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant calculates the contact force as 80.52N and the coefficient of friction as 0.393, but notes a discrepancy with the textbook answer of 92.2N.
  • Multiple participants assert that the reaction force (R) and net force (F) calculations are incorrect, specifically questioning the treatment of the 20N applied force in relation to the incline.
  • Some participants provide hints about the system being in static equilibrium, suggesting that the forces need to be resolved correctly in both the parallel and perpendicular directions to the incline.
  • One participant emphasizes the importance of understanding that the 20N force is horizontal with respect to the Earth’s surface, which affects the calculations.
  • A later reply indicates that after re-evaluating the calculations, the participant arrives at F=33.7N and R=85.8N, confirming the coefficient of friction as 0.393.

Areas of Agreement / Disagreement

Participants express disagreement on the calculations of forces and the interpretation of the problem statement, particularly regarding the components of the applied force. The discussion remains unresolved as participants have differing views on the correct approach and calculations.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the forces acting on the incline and the definitions of the components of the applied force. Some calculations and interpretations remain unverified.

Shah 72
MHB
Messages
274
Reaction score
0
View attachment 11145
It's the 10th question. Iam getting the ans for R=90cos34= 74.6 and F=-30.3N, so I get total contact force by using the formula c= sqroot(f^2+R^2)= 80.52N
The ans in the textbook is 92.2N. Iam not getting the right ans for coefficient of friction also which is 0.393
 
Mathematics news on Phys.org
Attachment doesn't show ...
 
skeeter said:
Attachment doesn't show ...
Iam so sorry.
20210513_222544.jpg
 
I get $\mu = 0.393$ ...

FBD_incline.jpg
 
Shah 72 said:
Can you pls show me the working

no.

I've provided the correct FBD ... this one is on you.

Hint: the system is in static equilibrium in both the parallel & perpendicular directions respective to the incline.
 
skeeter said:
no.

I've provided the correct FBD ... this one is on you.

Hint: the system is in static equilibrium in both the parallel & perpendicular directions respective to the incline.
R=90cos34
F=90sin34-20
Mu=0.406
I don't get the right ans
 
R is incorrect … what about the component of the 20N applied force perpendicular to the incline?

F net is incorrect … the component of the 20N applied force parallel to the incline is not 20.
 
skeeter said:
R is incorrect … what about the component of the 20N applied force perpendicular to the incline?

F net is incorrect … the component of the 20N applied force parallel to the incline is not 20.
R+20sin34= 90cos34
Is this the way to do?
 
  • #10
skeeter said:
R is incorrect … what about the component of the 20N applied force perpendicular to the incline?

F net is incorrect … the component of the 20N applied force parallel to the incline is not 20.
20210514_092813.jpg
 
  • #11
The problem statement says the 20N force is horizontal … that would be w/respect to the Earth’s surface, not the surface of the incline.

The reaction force in your diagram is also incorrect.

Your FBD looks nothing like the one I posted.

If you still can’t get the correct value for $\mu$, I recommend you seek assistance from your instructor.

I’m done.
 
  • #12
skeeter said:
The problem statement says the 20N force is horizontal … that would be w/respect to the Earth’s surface, not the surface of the incline.

The reaction force in your diagram is also incorrect.

Your FBD looks nothing like the one I posted.

If you still can’t get the correct value for $\mu$, I recommend you seek assistance from your instructor.

I’m done.
Ok no problem. I will try to work it out. Thank you!
 
  • #13
skeeter said:
The problem statement says the 20N force is horizontal … that would be w/respect to the Earth’s surface, not the surface of the incline.

The reaction force in your diagram is also incorrect.

Your FBD looks nothing like the one I posted.

If you still can’t get the correct value for $\mu$, I recommend you seek assistance from your instructor.

I’m done.
I got the ans. So F= 33.7N and R=85.8N
I got the ans 0.393.
Thank you so much!
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 8 ·
Replies
8
Views
1K
  • · Replies 4 ·
Replies
4
Views
1K
Replies
5
Views
1K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
Replies
2
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 37 ·
2
Replies
37
Views
2K