Question

If the strings are inextensible and pulleys are frictionless, the speed of point $G$ on block $M$ is

• A. $50\text{m/s}$
• B. $60\text{m/s}$
• C. $70\text{m/s}$
• D. $80\text{m/s}$

Answer 1

The correct option is C $70\text{m/s}$

For string $ABCD$, since the pulley is fixed
$V_A=V_B=V_C=V_D=10\text{m/s}$ (In terms of magnitude)
Taking velocity in upward direction to be positive and negative for downward direction.
$\Rightarrow V_D=10\text{m/s}\uparrow$
Now $V_D=\frac{V_H+V_E}{2}$
$V_H=-10m/s\downarrow$
$+10=\frac{-10+V_E}{2}\Rightarrow V_E=30\text{m/s}\uparrow$
Now $V_E=\frac{V_F+V_G}{2}\Rightarrow 30=\frac{-10+V_G}{2}$
$\Rightarrow 60+10=V_G$
$\Rightarrow V_G=70\text{m/s}\uparrow$