Question

In the system shown in fig. 6.373, $m_A$ = 4m, $m_B$ = 3m, and $m_C$ = 8m. Friction is absent everywhere. String is inextensible and light. If the system is released from rest, then the tension in the string is

• A. 1.7 mg
• B. 5.8 mg
• C. 4.7 mg
• D. 3.2 mg

Answer 1

Answer: (A)

1.7 mg

OPTION - A is correct

Equations of motion for the blocks -

Block B

$T=3ma-\left(i\right)$

For block A

$4mg-T=4ma$

$\begin{array}{cc}4mg-3ma& =4ma\\ 7ma& =4mg\end{array}$

$a=\frac{4}{7}g$

Putting value of a in eqn (i)

$T=3m\times \frac{4}{7}g=\frac{12}{7}mg$

$T=1.7mgN$