Solve Kinematics Problem: Find Acceleration for 2.7kg Blocks on Inclined Pulley

[pb23me]

Homework Statement

there are two blocks on a pully connected by a cable. one is on an incline and the other hangs in the air-see attatched photo. M1 = M2= 2.7kgs ; theta =34 ; coeffcient kinetic friction=.15 find acceleration

Homework Equations

Fmax=N(coefficient kinetic friction)
Fnet=ma

The Attempt at a Solution

i assumed block B was going down, wrote down three Fnet equations.Fnet1y=mgcos(theta)-mgcos(theta)=0 ; Fnet1x=T-mgcos(theta)(coefficient kinetic fr)=Ma ; F2=mg-T=Ma therefore T=mg-ma plugged it in the other equation and solved for acceleration. i got 4.3m/s^2 I am curious about solving for the force of friction... i thought it was N(coefficient static fr) in this case i have N=mgcos(theta) is this correct?

 

[tiny-tim]

hi pb23me!

(have a theta: θ and a mu: µ and try using the X² and X₂ icons just above the Reply box )

Can you write it out more clearly? It's difficult to check as it is.

(But I think you've left out the component of gravity along the slope.)

And yes, there's no acceleration perpendicular to the slope, so F = ma = 0 in that direction gives you N - mgcosθ = 0.

 

[pb23me]

well my only real question is what is the force due to friction? is it µ*mgcos\theta or µ*mgsin\theta
or is this equation correct ∑Fx=T-mg(cosθ)µ this is the equation for the block on the incline

 

[pb23me]

1)∑Fy=mgcosθ -mgcosθ=0
2)∑Fx=T-mg(cosθ)µ=ma
3)∑F=mg-T=ma
1&2 are for the block on the incline

 

[tiny-tim]

well my only real question is what is the force due to friction? is it µ*mgcos\theta or µ*mgsin\theta

It's µN, whatever that happens to be.

or is this equation correct ∑Fx=T-mg(cosθ)µ this is the equation for the block on the incline

As I said before, you've left out the component of mg along the slope.

(not the friction force, the gravity itself, which would be there even if the slope was smooth)

 

[pb23me]

oh are you telling me that gravity is acting dwn and to the rght? i think i see what u mean

 

[tiny-tim]

It's what gravity does best!

I'm off to bed now …

goodnight! :zzz:​

 

[pb23me]

thanx for the help:)