Question:
A healthy young man standing at a distance of $7 \mathrm{~m}$ from a $11: 8 \mathrm{~m}$ high building sees a kid slipping from the top floor. With what speed (assumed uniform) should he run to catch the kid at the arms height $(1.8 \mathrm{~m})$ ?
Solution:
For kid,
$\mathrm{u}=0 ; \mathrm{a}=\mathrm{g} ; \mathrm{s}=11.8-1.8$
$\mathrm{s}=10 \mathrm{~m}$
$s=u t+{ }^{\frac{1}{2}} a t^{2}$
$10=0+\frac{1}{2}(g) t^{2}$
$t=1.42 \mathrm{sec}$
In this time, man has to reach building
Speed $=\frac{\text { cistance }}{\text { time }}=1.42$
$=4.9 \mathrm{~m} / \mathrm{s}$
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