Tension problems

1. Feb 20, 2014

Garrett21

Can someone please tell me how my teacher got Acceleration of 1.44m/s^2?
I dont see how its even possible without another force acting on the object
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Attached Files:

• Physics.docx
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2. Feb 20, 2014

Staff: Mentor

Is it possible that the pulley has specified mass and radius in the problem statement?

Chet

3. Feb 21, 2014

Garrett21

No, she is just introducing this so there is no friction.. I was scratching my head while everyone was saying they got the same answer following instructions, but i vaguely disagreed with it so thats why im asking here.

4. Feb 21, 2014

oddjobmj

This seems to be a poorly designed problem. If you use F=ma and assume the pulley to be frictionless and massless you get a=(9.8)(5)/(15)=3.27 m/s^2

It seems that there is some assumed mass in the pulley though because they give you the distance it falls and the time it takes. Using those in the following kinematic equation yields an acceleration of 1.39 m/s^2 which is close:

x=x0+v0t+$\frac{1}{2}$at2

5. Feb 21, 2014

Staff: Mentor

What were the instructions? I got the same results as oddjobmj.

Chet

6. Feb 21, 2014

Garrett21

Just to find the acceleration at 1m... idk why this problem is annoying me so much but realistically on a test, i should write.. "this problem is not frictionless"

7. Feb 22, 2014

Staff: Mentor

One more thing. Are you sure the mass of A wasn't 30 Kg?

Chet

8. Feb 23, 2014

Garrett21

Yes 100% if the mass was 30kg would the acceleration be equal to what the problem states?

9. Feb 23, 2014

Staff: Mentor

Yes, pretty close.

chet