Dynamics: Minimum Force Problem

AI Thread Summary
The discussion revolves around solving a physics problem related to the minimum mass required for a system to remain at rest, given a coefficient of static friction of 0.100. The user JM92 seeks assistance in calculating the smallest mass M, with the correct answer being 4.98 kg. Clarifications were made regarding the placement of the friction force in the diagram, which initially caused confusion. After correcting the direction of the friction force, JM92 successfully arrived at the correct solution. The thread highlights the importance of accurately representing forces in physics problems to avoid miscalculations.
JM92
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Hi, nice to meet everybody here at physicsforums.com! I'm JM92 and I have a physics problem I need help with.

Homework Statement



Find the smallest value of the mass M for which the system will remain at rest given that the coefficient of static friction is 0.100
[PLAIN]http://img695.imageshack.us/img695/6328/physics2.jpg

Homework Equations



Fnet = ma
∑F(Horizontal) = 0
∑F(Vertical) = 0
Ff = μ・FN
Fgx = Fg・sinθ
Fgy = Fg・cosθ

The Attempt at a Solution


[PLAIN]http://img3.imageshack.us/img3/4139/physics11.jpg
I retyped and redrew everything with MS paint.. Hopefully that made it easier to read and not harder..:smile:

PS. The correct answer is 4.98kg.

Thank you for your help!

EDIT: Sorry, the thread title should be called "Minimum Mass Problem"
 
Last edited by a moderator:
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You've drawn Ff in the wrong place. M is the mass of the second block; if it is any smaller, the first block will slide down the incline.

How small can M be?
 
vertigo said:
You've drawn Ff in the wrong place. M is the mass of the second block; if it is any smaller, the first block will slide down the incline.

How small can M be?

Ohh! I was looking at it backwards, then. With Ff in the opposite direction, I got the correct answer. Thank you very much!
 

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