# Help Plz pulley problems

1. Jan 31, 2007

### blackice552

I have to problems that I'm having trouble with today I just can't seem to get my head around a lot of these physics concept so I'm finally coming here Plz help me. I've tried to do these problems and I just don't know what I'm doing.

1.We have two masses hanging from a pulley of inertia mp and constant frictional force f. One mass is 21.5g and the other is 39.8g. When data is taken, the slope of the 1/a vs. (m1 + m2) graph turns out to be 6.77 1/N. What is the value of the frictional force of the pulley? (2 decimals and UNITS!) (g=9.8m/s2)

We have two masses hanging from a pulley of inertia mp and constant frictional force f. One mass is 55.9g and the other is 41.8g. When data is taken, the intercept of the 1/a vs. (m1 + m2) graph turns out to be 0.04s2/m and the frictional force of the pulley 0.31N. What is the value of the inertia of the pulley? (2 decimals and SI UNITS!) (g=9.8m/s2) (If you get a negative answer type it in even though it doesnt make sense physically)

2. Relevant equations
These are the equations I have:

for no friction:
1/a = (m1 + m2)/((m1 -m2)g)

for a system with friction:
(m1 - m2)g - f = (m1 + m2 + mp)a

1/a = [(m1 + m2)/((m1-m2)g - f)] + [mp/((m1-m2)g -f))]

3. The attempt at a solution
My solutions were totally outrageous I have no idea what i'm doing frankly i've studied this stuff for hours and can't wrap my head around it