Question

the Cotton Express runs at a speed of 90 kmph. Its length is 240 m and it passes a man, walking at 10 kmph in the same direction, in "a" seconds. Determine the value of "a".

Answer 1

Hello,

Answer: a = 10.8

11 seconds approx are taken by train to pass that man.

Solution:
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• Speed of train = 90 km/h

• Length of train = 240 m

• Speed of man = 10 kmph

As both goes in same direction, So

Relative speed of train is 90-10= 80 kmph

Time taken to pass that man = length of train/relative speed of train

Length of train in km = 240/1000=0.24 km

Time taken to pass that man = 0.24/80 hours

Time taken in seconds

=
$\frac{0.24}{80} \times 60 \times 60 \\ \\ = 10.8 \: \: sec$

Hope it helps you.

Answer 2

speed of Cotton Express = 90km/h
speed of man = 10 km/h
length of cotton express is 240m or 0.24km


we know, if two particles move in same direction with speed $v_1$ and $v_2$ then, relative speed of 1st particle worn respect to 2nd is $v_{12}=|v_1-v_2|$.

here cotton express and man move in same direction. so, relative speed = 90 - 10
= 80 km/h

now, time taken = distance covered/relative speed
= (0.24)/80 = 0.003 hrs
= 0.003 × 60 × 60 = 10.8 sec