Question

A body is thrown up in a lift with a velocity $5 \, m \, s^{- 1}$ relative to the lift and the time of flight is found to be $0.8 \, s$ . The acceleration with which the lift is moving up is $\left(\right.g=10 \, m \, s^{- 2}\left.\right)$

• A. $1.5 \, ms^{- 2}$
• B. $2 \, ms^{- 2}$
• C. $2.5 \, ms^{- 2}$
• D. $3 \, ms^{- 2}$

Answer 1

Answer: (C)

Acceleration of body w. r. t. lift $=-(g \, +a)$
$\therefore $ Time of flight of body, $t \, = \, \frac{2 u}{g + a}$
$\Rightarrow a=\frac{2 u - g t}{t}=\frac{\left(\right. 2 \times 5 \left.\right) - \left(\right. 10 \times 0.8 \left.\right)}{0.8} \, = \, 2.5 \, ms^{- 2}$