I had this problem on a test I took last week, which our professor recently returned to us. Everyone has been getting the answer 3.33, but I'm not sure if it's correct. I got it wrong on the test. Here is the problem:(adsbygoogle = window.adsbygoogle || []).push({});

Given:

M1:5kg

Theta:60*

Coefficient of static friction:0.4

http://files.nicktiberi.com/files/inclinedplane.gif

Excuse the crude diagram, but it was either that or my sloppy handwriting from my test. Anyway, without further ado, the objective of the problem is:Find the minimum mass M2 such that the blocks do not move.

Here's my force analysis.

M2 vertical forces:T - M2g = 0

M1 horizontal forces:M1g[sin(theta)] - T - fs = 0

M2 vertical forces:N - M1g[cos(theta)] = 0

fs = mu static * N

fs = (.4)(24.5) = 9.8

Then, setting the two tensions equal to each other, I get:

M2g = M1g[sin(theta)] - fs

M2 = (M1g[sin(theta)] - fs) / g

After subbing all the numbers in, I get M2 = 3.33; according to one kid, he put 3.33 on his test but got it marked wrong. I really don't know any other way of doing this problem. Any help would be great.

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# Homework Help: Simple Mechanics Problem

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