Question

A man standing on a platform 225 m long notices that a train travelling at a unifor speed
passes him in 6 s and passes by the platform in 21 s.find (i)the length of the train and (ii) the speed of the train
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Answer 1

Answer:

Length of train = L

length of platform= 225m

time taken by train to cross the man = 6s

distance travelled by train to cross the man = L

time taken to cross platform= 21s

distance travelled by train to cross the platform= (L+225)m

So, in order to travel {(L+225) - (L)}m, train takes (21 - 6) second

Or train travels 225m in 15 second

speed of train = 225/15 = 15 m/s

Length of train = speed of train × time taken to cross the man = 15 × 6 = 90m

Answer 2

According to the given question we have to find the length of the train and the speed of the train,

Let, length of the train be 'x',

And the length of the platform $=225m$

Time is taken to cover $225m$ = $21 sec$ ...(1)

Time is taken to cover $xm=6sec$...(2)

By equations (i) and (ii),

Time is taken to cover $225m$

$=>(21-6)=15sec$

And distance it will cover in 1 sec,

$=>\frac{225}{15}=15m$

So, the length of the train

$n=15\times6=90m$

Speed of the train is $15m/s.$