Question

Three equal weights of $3kg$ 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 $g=10m/se{c}^2$):

• A. $5N$
• B. $6N$
• C. $10N$
• D. $20N$

Answer 1

Answer: (D)

$20N$

Let us take the three masses and the strings as a $system$.

Let the tension in the string be $T$.

Equation of motion are as follows-

$T-mg=ma$

$2mg-T=2ma$

$\Rightarrow$ $a=\frac{g}{3}$.

Now let us work from the ground reference for the block $|||$

Let tension in this string be $T_1$

equation of its motion is-

$mg-T_1=ma$

$\Rightarrow$ $T_1=\frac{2mg}{3}$

$T_1=20N$