Question

Three equal weights $A,B$ and $C$ of mass $2\text{kg}$ each are hanging on a string passing over a fixed pulley which is frictionless as shown in figure. The tension in the string connecting weight $B$ and $C$ is ?

• A. Zero
• B. $13\text{N}$
• C. $3.3\text{N}$
• D. $19.6\text{N}$

Answer 1

The correct option is B $13\text{N}$

Taking blocks A, B, C and the connected strings as a system,

Acceleration of system
$a=\frac{\text{Net pulling force}}{\text{Total mass}}=\frac{4g-2g}{6}=\frac{g}{3}$
Equation of motion of block $C$ is
$m_{c}g-T_{BC}=m_{c}a$
$\therefore T_{BC}=m_c(g-a)$
$=2(9.8-\frac{9.8}{3})=13\text{N}$