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firework218

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## Homework Statement

Three boxes are connected by strings of constant length. (A--B--C--> F) An applied force F acts horizontal in the positive x direction. mc=5kg, mb=2mc, ma=2mb. The coefficients of static and kinetic friction are 0.2 and 0.1 respectively and are the same for each box. The boxes are initially at rest.

1) What is the magnitude of the maximum force that can be applied without causing the boxes to move?

2) The magnitude of the applied force is varied until the boxes are moving to the right at a constant speed of 2m/s. What is the magnitude of the force when the boxes are moving at this constant speed?

3) The magnitude of the applied force is varied until the boxes are moving to the right at a constant speed of 2m/s. What is the magnitude of the tension in the string connecting A and B?

4) The applied force is adjusted so that the boxes accelerate to the right at a rate of 2m/s^2. What is the magnitude of the applied force?

## Homework Equations

F=ma

## The Attempt at a Solution

mc=5kg

mb=10kg

ma=20kg

mtotal=35kg

us=.2

uk=.1

1) 20*9.8 + 10*9.8 + 5*9.8 = 343

343*.2 = 68.6N

2) and 3) I'm not really understanding. I know F=ma, but a isn't given; v=2m/s. And I don't even know where to begin with tension.

4) F=35*2 = 70N

Thanks for your help in advance.