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7. MOTION
medium
An aeroplane lands at $216\, km\, h ^{-1}$ and stops after covering a runway of $2\, km .$ Calculate the acceleration and the time, in which its comes to rest.
Option A
Option B
Option C
Option D
Solution
$u=216 km h ^{-1}=60 m s ^{-1} ; \quad v=0 ; S =2 km$
$=2000 m ; a=? ; t=?$
$(i)$ Applying $v^{2}-u^{2}=2 aS,$ we have
$(0)^{2}-(60)^{2}=2 \times a \times 2000$
$a=-\frac{3600}{4000}=-0.90 m s ^{-2}$
$(ii)$ Applying $v=u+a t$
$0=60-0.90 t$
$0.90 t=60$ or $t=\frac{60}{0.90}=66.67 s$
Standard 9
Science
