Newton's Laws of motion problem

  • Thread starter sepah50
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  • #1
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Homework Statement



A block weighing 70.0 N rests on a plane inclined at 25.0° to the horizontal. A force F is applied to the object at 35.0° to the horizontal, pushing it upward on the plane. The coefficients of static and kinetic friction between the block and the plane are, respectively, 0.333 and 0.156.

What is the minimum value of F that will prevent the block from slipping down the plane?

Homework Equations



[tex]\sum[/tex]Fy= Sum of all Forces = Newton's Second Law



The Attempt at a Solution



So in the beginning I draw the Angles and make a Free Body Diagram. I sum up all the forces which is
[tex]\sum[/tex]Fy = [tex]\eta[/tex] + Fsin(10) - 70cos(25) = may

may is 0 since block is not moving away from the plane

what I get then is [tex]\eta[/tex]= .173648F - 63.4415

After this point I know I have to find Fsmax which equals [tex]\mu[/tex]s[tex]\eta[/tex]. After this part I get lost but I can't find [tex]\eta[/tex][tex]\mu[/tex]s
From what I remember [tex]\mu[/tex][tex]\eta[/tex]s = mg*sin[tex]\theta[/tex]. Hope somebody can help!
 

Answers and Replies

  • #2
alphysicist
Homework Helper
2,238
2
Hi sepah50,

Homework Statement



A block weighing 70.0 N rests on a plane inclined at 25.0° to the horizontal. A force F is applied to the object at 35.0° to the horizontal, pushing it upward on the plane. The coefficients of static and kinetic friction between the block and the plane are, respectively, 0.333 and 0.156.

What is the minimum value of F that will prevent the block from slipping down the plane?

Homework Equations



[tex]\sum[/tex]Fy= Sum of all Forces = Newton's Second Law



The Attempt at a Solution



So in the beginning I draw the Angles and make a Free Body Diagram. I sum up all the forces which is
[tex]\sum[/tex]Fy = [tex]\eta[/tex] + Fsin(10) - 70cos(25) = may

may is 0 since block is not moving away from the plane

what I get then is [tex]\eta[/tex]= .173648F - 63.4415

I think you have a couple of sign errors here.

After this point I know I have to find Fsmax which equals [tex]\mu[/tex]s[tex]\eta[/tex]. After this part I get lost but I can't find [tex]\eta[/tex][tex]\mu[/tex]s

When you summed up all the forces, you did it only in the y-direction (perpendicular to the plane). What is the sum of the forces in the x-direction (parallel to the plane)?

From what I remember [tex]\mu[/tex][tex]\eta[/tex]s = mg*sin[tex]\theta[/tex]. Hope somebody can help!
 
  • #3
5
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Thanks!! :)
 
  • #4
1
0
thanks
 

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