Jule J.

asked • 10/28/20

Free Body Diagram

A block with a mass of m rests on a rough surface and is subject to two forces acting on it. The first force is directed in the negative x-direction. The second acts on the body at an angle θ measured from horizontal, as shown. If necessary, use Fs and Fk for the forces of static and kinetic friction.


Could someone explain how I should draw it and if I should use fs and/or Fk and which direction that should go in . I already have the first and second forces drawn


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Scott D. answered • 10/28/20

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I can't see the diagram, so I have to assume the surface is horizontal. Draw weight (Fg) straight down and normal force (FN) straight up (the same length as Fg). It says the block is at rest so the force of static friction is in play and must point in the opposite direction of the horizontal component of the applied force (FA). And the horizontal component of the applied force should be drawn the same length as the Fs. The horizontal component mentioned is calculated by (FA)(cos θ).

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Jule J.

i am still confused on where fs should be pointing should it be opposite of the first force or the second force
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10/28/20

Belisario G.

tutor
Friction should oppose the sense of motion
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10/28/20

Jule J.

but there are two forces and i put it opposite of the first force and it is still telling me its wrong
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10/28/20

Jule J.

https://www.google.com/search?q=A+block+with+a+mass+of+m+rests+on+a+rough+surface+and+is+subject+to+two+forces+acting+on+it.+The+first+force+is+directed+in+the+negative+x-direction.+The+second+acts+on+the+body+at+an+angle+%CE%B8+measured+from+horizontal,+as+shown.+If+necessary,+use+Fs+and+Fk+for+the+forces+of+static+and+kinetic+friction.&sxsrf=ALeKk02rA8hVrKDacSXxPS_Eicc5CnMC6A:1603903496541&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiF66iR3tfsAhXK6Z4KHVpZDroQ_AUoAXoECAwQAw&cshid=1603903544642521&biw=1280&bih=689#imgrc=NrUXBYDAu_UbhM
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10/28/20

Jule J.

^that is a link to the diagram I found
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10/28/20

Scott D.

tutor
Belisario is right, but in this case it seems there is no motion. Again, I can't see the diagram, but if the force in the negative x direction is opposite the applied force, the negative x force probably represents Fs.
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10/28/20

Scott D.

tutor
The link does not come through. Are the two forces mentioned pointing in opposite directions?
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10/28/20

Jule J.

heres the link: https://www.google.com/search?q=A+block+with+a+mass+of+m+rests+on+a+rough+surface+and+is+subject+to+two+forces+acting+on+it.+The+first+force+is+directed+in+the+negative+x-direction.+The+second+acts+on+the+body+at+an+angle+%CE%B8+measured+from+horizontal,+as+shown.+If+necessary,+use+Fs+and+Fk+for+the+forces+of+static+and+kinetic+friction.&sxsrf=ALeKk02rA8hVrKDacSXxPS_Eicc5CnMC6A:1603903496541&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiF66iR3tfsAhXK6Z4KHVpZDroQ_AUoAXoECAwQAw&cshid=1603903544642521&biw=1280&bih=689#imgrc=NrUXBYDAu_UbhM
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10/28/20

Jule J.

force 1 is pointing in the negative direction at 180 degrees and force 2 is pointing at around 315 degrees in the 4th quadrant
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10/28/20

Scott D.

tutor
OK that is the way I visualized it. If the force arrows are about the same length, then I think the negative x force is supposed to be Fs.
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10/28/20

Jule J.

force 1 << force 2
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10/28/20

Jule J.

i finally got it correct thank you for your help
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10/28/20

Scott D.

tutor
Glad to hear it!
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10/28/20

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