Question

Two blocks A and B of masses $2.9kg$ and $1.9kg$ respectively are suspended with the help of two inextensible wires each of the length $1m$ from a rigid support as shown in the figure. The mass of the upper wire is negligible and that of the lower wire $0.2kg/m$. This system of block, wires and rigid support is moving upwards with an acceleration of $0.2m/s^2$. The tension at the midpoint C and D of the lower and the upper wires will be respectively:

• A. $20N,10N$
• B. $20N,50N$
• C. $20N,40N$
• D. $50N,20N$

Answer 1

Answer: (B)

$20N,50N$

For Tension at C:

$(M_B+m_{BC})a=T_C-M_{A}g$

Given: $a=0.2m/s^2$, $m_{BC}=\frac{1}{2}\times 0.2=0.1kg$, for wire BC.

$T_C=(1.9+0.1)(0.2+9.8)=20N$

For tension at D:

$(M_A+M_B+m_{AB})a=T_D-(M_A+M_B+m_w)g$

Given: $m_{AB}=0.2kg$ for wire AB.

$T_D=(2.9+1.9+0.2)(0.2+9.8)=50N$

$\therefore T_C=20N\text{and}{T}_D=50N$