Question

In the figure shown the velocity of lift is $2ms^{- 1}$ upwards while the string is winding on the motor shaft with velocity $2ms^{- 1}$ and block $A$ is moving downwards with a velocity of $2ms^{- 1}$ , then find out the velocity of block $B$ .

• A. $2ms^{- 1}\uparrow$
• B. $2ms^{- 1}\downarrow$
• C. $4 \, m \, s^{- 1}\downarrow$
• D. $8 \, m \, s^{- 1}\uparrow$

Answer 1

Answer: (D)

Let, $v_{B} =$ velocity of block $B$
$v_{\frac{A}{L}} =$ velocity of block $A$ with respect to lift
$v_{L} =$ velocity of lift
$v_{B} = - v_{\frac{A}{L}} + v_{L} + v_{\text{winding}}$
$= - \left(\right. v_{A} - v_{L} \left.\right) + v_{L} + v_{\text{winding}}$
$= - \left(\right. - 2 - 2 \left.\right) + 2 + 2$
$=8ms^{- 1}$