Question

Three blocks $A,B$ and $C$ of equal weights of mass $2\text{kg}$ each are hanging on a string passing over a fixed pulley as shown in figure. What is the tension in the string connected between block $B$ and $C$?

• A. $12\text{N}$
• B. $13.33\text{N}$
• C. $3.3\text{N}$
• D. $19.6\text{N}$

Answer 1

The correct option is B $13.33\text{N}$

For finding the acceleration of the system, we take the block $B$ and $C$ together and we use force equation.


$a_{sys}=\frac{4g-2g}{6}=\frac{g}{3}=\frac{10}{3}\text{m/s^2}$

Now for the tention in the string $BC$ we draw the FBD of the block $C$ and it will also have the same acceleration as $\frac{10}{3}{\text{m/s}}^2$

We get , $mg-T=ma$
$\Rightarrow 2\times 10-T=2\times \frac{10}{3}$
$\Rightarrow T=\frac{40}{3}=13.33\text{N}$

Hence option B is the correct answer