Question

From a $10m$ high building a stone ${}^{\prime }{A}^{\prime }$ is dropped $\&$ simultaneously another stone ${}^{\prime }{B}^{\prime }$ is thrown horizontally with an initial speed of $5m/s$. Which one of the following statement is true?

• A. It is not possible to calculate which one of two stones will reach ground first
• B. Both stones ${}^{\prime }{A}^{\prime }\&{}^{\prime }{B}^{\prime }$ will reach the ground simultaneously
• C. ${}^{\prime }{A}^{\prime }$ stones reach the ground earlier than ${}^{\prime }{B}^{\prime }$
• D. ${}^{\prime }{B}^{\prime }$ stones reach the ground earlier than ${}^{\prime }{A}^{\prime }$

Answer 1

The correct option is B Both stones ${}^{\prime }{A}^{\prime }\&{}^{\prime }{B}^{\prime }$ will reach the ground simultaneously

Since in both case the height of building and downward acceleration $g$ is same. So both stones reach simultaneously i.e.,
From second kinematic equation, $S=ut+\frac{1}{2}g{t}^2\Rightarrow u=0\Rightarrow S=\frac{1}{2}g{t}^2$
$\Rightarrow 10=\frac{1}{2}10\times t^2$
Or, $t=\sqrt{2}s$ for both stone.