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2.Motion in Straight Line
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Two stones are thrown up simultaneously from the edge of a cliff $240\ m$ high with initial speed of $10\ m/s$ and $40\ m/s$ respectively. Which of the following graph best represents the time variation of relative position of the second stone with respect to the first ?
(Assume stones do not rebound after hitting the ground and neglect air resistance, take $g = 10\ m/ s^2$)
(The figures are schematic and not drawn to scale)
A
B
C
D
(JEE MAIN-2015)
Solution
$\begin{array}{l}
{y_1} = 10t – 5{t^2};{y_2} = 40t – 5{t^2}\\
for\,\,\,\,\,{y_1} = – 240m,t = 8s\\
\therefore \,\,\,\,\,\,\,\,\,\,{y_2} – {y_1} = 30t\,for\,t \le 8s.\\
for\,\,\,\,\,\,t > 8s.\\
{y_2} – {y_1} = 240 – 40t – \frac{1}{2}g{t^2}
\end{array}$
Standard 11
Physics
