1. Jan 16, 2010

### tigerwoods99

1. The problem statement, all variables and given/known data
A uniform ladder of mass m and length L leans at an angle θ against a frictionless wall, Fig. 9-61. If the coefficient of static friction between the ladder and the ground is 0.43, what is the minimum angle at which the ladder will not slip?

Pic:
http://www.webassign.net/giancoli5/9_61.gif

2. Relevant equations

?? tan(theta) = .43?

3. The attempt at a solution

23.26

2. Jan 16, 2010

### tiny-tim

Hi tigerwoods99!

(have a theta: θ )
I don't think so.

What equations did you use?

3. Jan 16, 2010

### tigerwoods99

Hi! I am really not sure its more or less a wild guess using trigonometric functions.

4. Jan 17, 2010

### tiny-tim

(just got up :zzz: …)
thought so!

ok … call the normal reaction force (from the ground) N, and the horizontal reaction force H …

how much is N?

5. Jan 17, 2010

### tigerwoods99

I think this is right.

τorque = 1/2mgx - FNx + Ffy

at max angle
μmgy = 1/2mgx

the maximum angle is θ = tan−1(1/(2μ))

6. Jan 17, 2010

### tiny-tim

Yup!

Easy, isn't it?

7. Jan 17, 2010

### tigerwoods99

haha yea i guess.. though i haven't learned this yet so i had to figure it out.