- #1

hyddro

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## Homework Statement

The two blocks in the figure are connected by a massless rope that passes over a pulley. The pulley is 14cm in diameter and has a mass of 2.4 kg. As the pulley turns, friction at the axle exerts a torque of magnitude 0.54 Nm .

## Homework Equations

so m1 = 4.0kg

m2= 2.0 kg

M = 2.4kg

r= 0.07m

Tf (torque due to friction) = 0.54 Nm

ƩFy (for mass 1)= T2 - m1*g

m1*ay1 +m1*g= T2 so T2 = m1(ay1+g) this becomes

**T2= m1(ay + g)**

ƩFy (for mass 2)= T1 - m2*g

m1*ay2 + m2*g = T1 so T1 = m2(ay2 + g)

but since ay1 = -ay2 = ay this becomes

**T1 = m2(g - ay)**

Ʃτ= T2*R - T1*R - Tf

## The Attempt at a Solution

Using what i put up there i get the following formula

τnet = R(T2 - T1) - Tf = R(m1(ay+g) - m2(g-ay)) - Tf ... equation 1

since τ= Iα, I= 1/2 MR^2 and since α= -ay/R

equation 1 becomes..

1/2MR^2 * (-ay)R = R(m1(ay+g) - m2(g-ay)) - Tf ... solving for ay with the given data i found ay=-1.65 and thus using the kinematic equation i found Δt= 1.55s but this is wrong.. :( i would appreciate if anyone points out my error or mistake, thanks

EDIT: sorry about this, they are asking us to find the time it takes for mass 1 to hit the floor, starting at rest.

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