Solving Mechanics Friction Problem: How to Calculate Contact Force

[Shah 72]

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

 

[skeeter]

Attachment doesn't show ...

 

[Shah 72]

Attachment doesn't show ...

Iam so sorry.

 

[skeeter]

I get $\mu = 0.393$ ...

 

[Shah 72]

I get $\mu = 0.393$ ...

View attachment 11147

Can you pls show me the working

 

[skeeter]

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.

 

[Shah 72]

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

 

[skeeter]

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.

 

[Shah 72]

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?

 

[Shah 72]

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]

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.

 

[Shah 72]

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!

 

[Shah 72]

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!