Block-on-Block attached by String to Block in Pulley on Incline

[Keena]

Hi all,

The problem is shown below - but no answer was given to this, and the teacher did not plan on taking it up, since it was optional extra practice.

My attempt at a solution: http://imgur.com/DmrgMMO, my final answer was 2.76 kg.

I was wondering if this was right or wrong, and if anyone could show me the proper steps.

Thanks for your time.

 

[SammyS]

Hi all,

The problem is shown below - but no answer was given to this, and the teacher did not plan on taking it up, since it was optional extra practice.

My attempt at a solution: http://imgur.com/DmrgMMO, my final answer was 2.76 kg.

I was wondering if this was right or wrong, and if anyone could show me the proper steps.

Thanks for your time.

Your solution for the maximum acceleration of Block C looks fine.

I haven't gone through the rest of your solution, but with that, it should be pretty straight formard to fin the force necessary to accelerate Block B & C at that value.
...

 

[Keena]

Ah, quick specific question, my calculation for the X component of the Fg for Block B+C, was done by adding up both masses.

But looking at example 3 here: http://www.physicsclassroom.com/class/newtlaws/Lesson-3/Double-Trouble

Should I have just calculated X component for Fg of Block B+C with just the mass of B?

 

[SammyS]

Ah, quick specific question, my calculation for the X component of the Fg for Block B+C, was done by adding up both masses.

But looking at example 3 here: http://www.physicsclassroom.com/class/newtlaws/Lesson-3/Double-Trouble

Should I have just calculated X component for Fg of Block B+C with just the mass of B?

Block C is stationary with respect to Block B, so you can threat them as a single object.

 

[Keena]

Thanks very much.

Everything's clear to me now.