# Friction problem

1. Feb 15, 2010

### lockedup

1. The problem statement, all variables and given/known datamass 1 is 2.0 kg, the static and kinetic coefficients of friction are .30 and .20 respectively.

a) What is mass 2 if it travels uniformly upward?
b) Downward?
c) mass 1 and 2 are at rest?

2. Relevant equations

3. The attempt at a solution

Part c is the easiest. Friction and Tension are going to be the same so $$m_{2} = \mu_{s}m_{1}$$.

Part a, I did the same thing about except I used $$\mu_{k}m_{1}$$.

Part b, $$m_{1}g = \mu_{k}m_{1}g$$
$$m_{2} = m_{1}/\mu_{k}$$

Is this right?

Why is it that I can ace Abstract Algebra but this gives me a headache?

2. Feb 16, 2010

### tiny-tim

Hi lockedup!

erm … what is the set-up?

3. Feb 16, 2010

### inutard

I'm guessing its a triangular slope of some sort with one mass on either side.

4. Feb 16, 2010

### tiny-tim

Hi inutard!
ah, but then we'd have heard about a θ

5. Feb 17, 2010

### inutard

Good point. Maybe its in the diagram that he is neglecting to show us (As he also mentions tension but he neglected to talk about a rope or string in his question).

6. Feb 18, 2010

### lockedup

Damn, I forgot to attach the picture! I'm a she BTW... lol

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7. Feb 18, 2010

### tiny-tim

(just got up :zzz: …)

Hi lockedup (f.)!

mmm … inutard guessed right!

ok then, there's a θ = 37º, which isn't in your equations …

put it in now …

what do you get?

8. Feb 18, 2010

### inutard

Pardon me about the gender mixup! Remember that theres not only frictional force opposing direction of motion but also a force to the bottom-left (depending on the angle) that is caused by the normal force on block m1