Three equal weights of $3 \mathrm{~kg}$ each are hanging on a string passing over a frictionless pulley as shown in figure. The tension in the string between masses II and III will be (Take $g=10 \mathrm{~m} / \mathrm{sec}^2$ )

• A

  $5 \mathrm{~N}$
• B

  $6 \mathrm{~N}$
• C

  $10 \mathrm{~N}$
• Correct answer
  D

  $20 \mathrm{~N}$

Solution

Three equal weights of $3 \mathrm{~kg}$ each are hanging on a string passing over a pulley as shown in figure. If $a$ is the common acceleration. $T-3 g=3 a$ (For mass I) $3 g+T_1-T=3 a$ (For mass II) $3 g-T_1=3 a$ (For mass III) Adding, above three equations $\begin{aligned} & 3 g=9 a, a=g / 3 \\ & T_1=3 g-3 a=3 g-g=2 g=20 \mathrm{~N}\end{aligned}$

Hence, the correct answer is option: 'D'.