Question

For the arrangement shown in the figure, the reading of spring balance is:

• A. $50N$
• B. $100N$
• C. $150N$
• D. None of the above

Answer 1

Answer: (D)

$\text{Step 1: Acceleration of system [Refer Fig.]}$

String and spring are massless

Apply Newton's second law on $5kg$

$\Sigma F=ma$

$T-5g=5a$ $....\left(1\right)$

Apply Newton's second law on $10kg$

$\Sigma F=ma$

$10g-T=10a$ $....\left(2\right)$

Adding equation $\left(1\right)$ and $\left(2\right)$

$a=\frac{5g}{15}=\frac{5\times 10}{15}=\frac{10}{3}m/s^2$

$\text{Step 2: Reading of spring balance}$

Reading of spring balance will be force responsible for its elongation.

Tension is responsible for the elongation of spring.

From equation (2)

$10g-T=10a$

$10\times 10-T=10\times \frac{10}{3}$ $\Rightarrow T=\frac{200}{3}N$