Question

As shown in figure two masses $15kg$ each are suspended through two strings tied to a spring balance after passing over frictionless pulleys. The reading the balance will be:

• A. $zero$
• B. $15kg$
• C. $30kg$
• D. $7.5kg$

Answer 1

Answer: (B)

$15kg$

let the tension in the string be $T$

$mg-T=ma$

system is at rest hence $a=0$

$T=mg$

let the extension in spring be $x$ then $F_x=kx$

at the end of spring balance and acceleration is zero

$F_x-T=0$

$F=T=mg$ that is $15kg.wt$