How Do You Calculate Mass 2 in Different Friction Scenarios?

[lockedup]

Homework Statement

mass 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?

Homework Equations

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?

 

[tiny-tim]

Hi lockedup!

erm … what is the set-up?

 

[inutard]

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

 

[tiny-tim]

Hi inutard!

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

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

 

[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).

 

[lockedup]

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

 

[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? ​

 

[inutard]

Pardon me about the gender mixup! Remember that there's 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