A metro train starts from rest and in five seconds achieves 108, km/h . After that it moves with con

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2.Motion in Straight Line

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A metro train starts from rest and in five seconds achieves $108\, km/h$. After that it moves with constant velocity and comes to rest after travelling $45\, m$ with uniform retardation. If total distance travelled is $395\,m$, then total time of travelling is.......$sec$

A

$12.2$

B

$15.3$

C

$9$

D

$17.2$

Solution

For last part $30^{2}=2 \times \mathrm{a} \times 45$

${\mathrm{a}=10 \mathrm{m} / \mathrm{s}^{2}}$

${\text { time }=\frac{30}{10}=3 \mathrm{sec}}$

For middle part

$t=\frac{275}{30}=9.2 \mathrm{sec}$

time $=17.2$ sec

Standard 11

Physics

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