Question

A stone is thrown vertically upward files past a window one second after it was thrown upward and after three seconds on its way downward. The height of the window above the ground is (Take $g=10m{s}^{-2}$)

• A. $20m$
• B. $15m$
• C. $10m$
• D. $5m$

Answer 1

The correct option is A $20m$

So, $AB$ time will be $1.5\sec .$
Final velocity at $B$ zero.
So,
$H=ut+\frac{1}{2}g{t}^2......\left(1\right)$
and total time is $OA=1+1.5=2.5\sec .$
used $v=u+gt$
$0=u-10\times 2.5$
$u=25m{s}^{-1}$
Now
$x=25\times 1-\frac{1}{2}\times 10\times 1^2$
$=25-5$
$x=20m$