# The tension in the line between A and B

1. Nov 5, 2007

### mariachy

1. The problem statement, all variables and given/known data
THREE IDENTICAL BLOCKS (A,B AND C) ARE BEING PULLED BY AN IDEAL STRING BY A HORIZONTAL FORCE F( PULLES THEM TO THE RIGHT). IT THE TENSION BETWEEN BLOCK B AND C IS T=3N, mass of each block= 0.4 kg ,I DONT KNOW HOW TO UPLOAD A PICTURE BUT THE BLOCKS ARE IN THE ORDER OF
A B C pUllED BY F IN THIS DIRECTION >

2. Relevant equations

A) FIND THE FORCE F
B) FIND THE TENSION BETWEEN BLOCK A AND B

3. The attempt at a solution

I TRIED F=MASS OF C* acc. + tension but i got a wrong answer
and for part b idont hav a clue plz guide me!!!

Last edited: Nov 5, 2007
2. Nov 5, 2007

### Staff: Mentor

Are the blocks moving at constant velocity, i.e. the acceleration is zero, or are they accelerating? What is the coefficient of friction?

The tension in the line between A and B will be one half of that in B and C, the then tension in the line attached to C must be 1.5 times that between B and C.

The friction force on each of A, B and C is $\mu$ mg, where m is the mass of A which is also the masses of B and C, and the friction force must = tension between A and B if the blocks are not accelerating.

3. Nov 5, 2007

### mariachy

thanks for ur responce

there is no friction

the blocks are at rest but when the force pulls them they starts to move
any thing else??

4. Nov 5, 2007

### Staff: Mentor

Ah, OK, then we can assume that the blocks are accelerating.

So the tension between B and C is related strictly to the resistance to motion of blocks A and B. The tension, 3 N, is due to the masses of A and B (0.4 + 0.4 kg) resisting the acceleration a. Now to find the acceleration, take the tension 3 N and divide by the masses of A and B.

The tension between A and B is still half that of the string between B and C, since the tension there is only due to the acceleration of mass A.

Then the tension or force pulling C must be mass (A+B+C)*a or the sum of the tensions between AB and BC.

5. Nov 5, 2007

thnx man