Question

The tension in the cable supporting a lift moving upwards is twice the tension when the lift moves downwards. What is the acceleration of the lift?

• A. g/4
• B. g/3
• C. g/2
• D. g

Answer 1

The correct option is B g/3

When the lift is moving upward



$\frac{w}{g}a=T-w$

$\therefore T_{up}=w[1+\frac{a}{g}]$

When the lift moving downwards



$\frac{w}{g}a=w-T$


$T_{down}=w[1-\frac{a}{g}]$

It is said that

$T_{up}=2T_{down}$

$w[1+\frac{a}{g}]=2w[1-\frac{a}{g}]$

$\therefore a=\frac{g}{3}$