# Homework Help: Simple yet I need refreshing

1. Mar 22, 2012

### 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..

1. The problem statement, all variables and given/known data
2 boxes, 10 KG and 20 KG with a coefficient of static friction of 0.4. calculate the angle each box begins to slide

2. Relevant equations

3. 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 ?

2. Mar 22, 2012

### BruceW

you've got it correct by using the equation tan(theta) = µs (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.

3. Mar 23, 2012

### 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 havent 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 :@