Question

Two blocks of mass $1kg$ and $2kg$ are connected by string AB of mass $1kg$. The blocks are placed on a smooth horizontal surface. Block of mass $1kg$ is pulled by a horizontal force $F$ of magnitude $8N$. Find the tension in the string at points A and B.

• A. $4N,6N$
• B. $3N,5N$
• C. $3N,4N$
• D. $5N,6N$

Answer 1

Answer: (A)

$4N,6N$

The total mass of the system is $m=2+1+1=4kg$

Let a be the acceleration of the system.

Thus, $ma=F$ or $4a=8$ or $a=2m/s^2$

The tension at A is $T_A=$ mass of left block $\times$ acceleration $=2\times 2=4N$

and tension at B is $T_B=$ (mass of left block + mass of string AB)$\times$ acceleration $=(2+1)\times 2=6N$