What is the angle of static friction for two boxes with different masses?

[quakedude]

Hello all! I am new to this forum, although I browse around here often, I recently took the plunge to make an account. I finished my college a few years ago and want to move back into schooling for uni so I need to do some courses over the next few months. please be patient, sometimes I forget the simplest of things. for instance..

I am not sure if this is a trick question, I have 2 boxes of different mass but same static friction... if I am not mistaken, I believe both boxes will begin to slide at the same angle, regardless of weight..

Homework Statement

2 boxes, 10 KG and 20 KG with a coefficient of static friction of 0.4. calculate the angle each box begins to slide

Homework Equations

The Attempt at a Solution

I would assume neither of the masses are taken into account for this so.. I did

∅=arctan⁡(µs)
∅=tan^(-1) ⁡(0.4)
∅=21.8°


therefore each box will begin to slide at any angle ABOVE 21.8 right ? I would assume the 21.8 is the MAX angle before they begin to slide. or am I missing something important ?

 

[BruceW]

you've got it correct by using the equation tan(theta) = µ_s (for maximum angle without sliding, 'theta'). If you want to understand more, then you can also derive this equation.

P.S. Welcome to physicsforums, I'm glad you've posted.

 

[quakedude]

awesome! thank you! I know this is simple stuff, I am just in need of refreshing, and need to get back into the (study ) zone that I haven't been in a few years.

thank you again, and it looks like I might be populating the calculus threads in a few weeks, that is my weakest subject :@