Question

Three equal blocks of mass $2$ kg each are hanging on a string passing over a fixed pulley as shown in the figure. What is the tension in the string connecting the weights $B$ and $C$?

• A. $zero$
• B. $13N$
• C. $3.3N$
• D. $19.6N$

Answer 1

Answer: (B)

$13N$

We can infer from the figure that on the right side of the pulley 2g N force acts downward and tension $T_1$ acts upward for the block C.

Hence, $2g-T_1=2a$ ....(1)

In the case of the block B above we have
$2g+T_1-T_2=2a$.................(2)
and In the case of block A above we have

$T_2-2g=2a$........(3)

adding eqn (1),(2) and (3) we have $2g=6a$

or $a=\frac{g}{3}$
But from eqn (1)
$2g-T_1=\frac{2g}{3}$
$T_1=\frac{4g}{3}=13N$

Thus, the tension between the string is $13N$