Question

In the system shown in figure all surfaces are smooth. String is massless and inextensible. Find acceleration $a$ of the system and tension $T$ in the string. ( $g=10m/s^2$)

• A. $\frac{40}{3}N$
• B. $20N$
• C. $25N$
• D. $50N$

Answer 1

Answer: (A)

$\frac{40}{3}N$

Here, weight of $2kg$ is perpendicular to motion (or $a$). Hence, it will not contribute in net pulling force. Only weight of $4kg$ block will be included.

$\therefore a=\frac{Netpullingforce}{Totalmass}$

$=\frac{\left(4\right)\left(10\right)}{(4+2)}$

$=\frac{20}{3}m/s^2$

For $T$, consider FBD of $4kg$ block. Writing equation of motion.

$40-T=4a$

$\therefore T=40-4a$

$=40-4\frac{20}{3}$

$=\frac{40}{3}N$