- #1

jamesweston0

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Hey all. I'm new to this forum and by the looks of it, a lot of you really know your physics. I was hoping for some help on this problem I can't figure out. I think I haven't fully grasped all the concepts involved in this question.

Determine the velocity of the 51-lb block A if the two blocks are released from rest and the 30-lb block B moves 2 ft up the incline. The coefficient of kinetic friction between both blocks and the inclined planes is u = 0.10.

(1/2)(m)(v)^2=KE

mgh=PE

Force of friction=(u)(Normal force)

Having trouble putting it all together as you'll see below.

Basically I think I am close but I am either missing something crucial or just misunderstand a concept. The first idea had in solving this was to just isolate the right side of the incline plane and solve for the tension in the rope. It was laid out like so:

Tension = Ffriction + Fparallel

I took all the forces on the block and set it equal to zero. Than solved for Tension. I assumed this was okay to do since there is no acceleration. Also I think the system is at rest after it moves up 2 ft.

I then looked at the other side of the incline. On this side, there are tension forces directed upwards, a friction force also upward, and Fparallel downward. I used the Work/energy equation to solve for velocity combining all of these. It looked like this:

(Fnormal)(2ft) - (Ffriction)(2ft) - (Tension)(2ft) = (1/2)(m)(v)^2

Basically I use this to solve for velocity. The answer I get is not correct. The reason why I didn't show you the numbers I used is that I am sure that I messed up somewhere in terms of concepts.

Looking at this, it doesn't really make much sense to me. It looks kind of like a jumbled mess. The thing is that I can do these sorts of problems when they're a bit more basic, but I think the fact that it's an incline on 2 sides with pulleys is really messing me up. If someone could explain how to do this, and also explain what's wrong in my thinking I will be so happy and thankful. I promise I won't disappear on replies.

Thanks!

## Homework Statement

Determine the velocity of the 51-lb block A if the two blocks are released from rest and the 30-lb block B moves 2 ft up the incline. The coefficient of kinetic friction between both blocks and the inclined planes is u = 0.10.

## Homework Equations

(1/2)(m)(v)^2=KE

mgh=PE

Force of friction=(u)(Normal force)

Having trouble putting it all together as you'll see below.

## The Attempt at a Solution

Basically I think I am close but I am either missing something crucial or just misunderstand a concept. The first idea had in solving this was to just isolate the right side of the incline plane and solve for the tension in the rope. It was laid out like so:

Tension = Ffriction + Fparallel

I took all the forces on the block and set it equal to zero. Than solved for Tension. I assumed this was okay to do since there is no acceleration. Also I think the system is at rest after it moves up 2 ft.

I then looked at the other side of the incline. On this side, there are tension forces directed upwards, a friction force also upward, and Fparallel downward. I used the Work/energy equation to solve for velocity combining all of these. It looked like this:

(Fnormal)(2ft) - (Ffriction)(2ft) - (Tension)(2ft) = (1/2)(m)(v)^2

Basically I use this to solve for velocity. The answer I get is not correct. The reason why I didn't show you the numbers I used is that I am sure that I messed up somewhere in terms of concepts.

Looking at this, it doesn't really make much sense to me. It looks kind of like a jumbled mess. The thing is that I can do these sorts of problems when they're a bit more basic, but I think the fact that it's an incline on 2 sides with pulleys is really messing me up. If someone could explain how to do this, and also explain what's wrong in my thinking I will be so happy and thankful. I promise I won't disappear on replies.

Thanks!

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