# Three blocks connected by strings

## Homework Statement

Three identical blocks, each of mass 0.6 kg, are connected by light strings. Assume that they lie on a frictionless, horizontal surface and are observed to have an acceleration of 4.0 m/s2 under the action of a force F.

## Homework Equations

Calculate F and two tension forces Tbc and Tab

## The Attempt at a Solution

by applying newton second law on each block and then by projection on xx axis, we get:
On A:
F-Tab=m*a----(1)
On B:
Tab-Tbc=m*a----(2)
On C:
Tbc=m*a----(3)

(1)+(2)+(3) $$\RightarrowF=3*m*a$$
F=7.2N

And then from (3) we have Tbc=m*a=0.6*4
Tbc=2.4N
From (1) we get -Tab=(m*a)-F
-Tab= (0.6*4)-7.2
Tab=4.8N

#### Attachments

• Three blocks.JPG
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Last edited:

PhanthomJay
Homework Helper
Gold Member
looks good! You can check your work by drawing FBD's of blocks A and B together, and B and C together, to see if your values check out..

what is FBD

Free Body Diagram. In this diagram, all the forces acting on the body are shown

This one ?

#### Attachments

• img001.jpg
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Yeah that is an FBD

I noticed that Tab is greater than Tbc
maybe this is always the case ?
also ..how to check?
i noticed that F=Tab+Tbc..maybe it's a coincidence?

PhanthomJay