Question

From the roof of a lift a $4kg$ block is suspended with the help of a light string. Another $2kg$ block is suspended from the bottom surface of the $4kg$ block with another light string. If the lift is moving up with uniform acceleration of $5m{s}^{-2}$, the tension in the string connecting the two blocks is: $[g=10m{s}^{-2}]$

• A. $10N$
• B. $20N$
• C. $30N$
• D. $90N$

Answer 1

Answer: (C)

$30N$

Solving In the frame of lift (non-inertial frame) each block will experience a pseudo force equal to its mass $\times$ acceleration of the lift in downward direction.

Hence, tension in the string, $T=mg$ of $2kg$ block $+$ pseudo force acting on it

$T=2\times 10+2\times 5=30N$

hence, option (c) is correct