Question

An elevator in which a man is standing is moving upwards with a speed of 10 m/s. If the man drops a coin from a height of 2.45 m from the floor of the elevator, it reaches the floor of the elevator after a time (g = 9.8 m/s2)

• A. $\sqrt{2}$
• B. $\frac{1}{\sqrt{2}}$
• C. $2s$
• D. $\frac{1}{2}s$

Answer 1

The correct option is B $\frac{1}{\sqrt{2}}$

Using the notations,
C : coin
E : Elevator
$a_{CE}=a_{CO}-a_{EO}$
$=-g-0$
$=-9.8m{s}^{-2}$
$u_{CE}=0m{s}^{-1}$
$s_{CE}=-2.45m$
We have,
$s_{CE}=u_{CE}t+\frac{1}{2}{a}_{CE}{t}^2-2.45=0+\frac{1}{2}(-9.8)t$
$\Rightarrow t^2=\frac{1}{2}\Rightarrow t=\frac{1}{\sqrt{2}}s$