The mass of a lift is $2000 \mathrm{~kg}$. When the tension in the supporting cable is $28000 \mathrm{~N}$,…
The mass of a lift is $2000 \mathrm{~kg}$. When the tension in the supporting cable is $28000 \mathrm{~N}$, then its acceleration is
$30 \mathrm{~ms}^{-2}$ downwards
$4 \mathrm{~ms}^{-2}$ upwards
$4 \mathrm{~ms}^{-2}$ downwards
$14 \mathrm{~ms}^{-2}$ upwards
Solution
Key Idea Apparent weight $>$ actual weight, then the lift is accelerating upward.
Here, lift is accelerating upward at the rate of $a$ Hence, equation of motion is written as
$\begin{gathered}
\mathrm{R}-\mathrm{mg}=\mathrm{ma} \\
28000-20000=2000 \mathrm{a} \\
\Rightarrow \mathrm{a}=\frac{8000}{2000}=4 \mathrm{~ms}^{-2} \text { upwards }
\end{gathered}$
