Question

Jammu express is moving in a speed of 20 km/hr . Jai is his car was moving in opposite direction with the speed of 5/18 m/s. In how much time does the jammu express cross jai completely id it is 700m long?

Answer 1

Answer:

lt will be 700m is 50 m is 36 s

Answer 2

Answer:

It takes 120 seconds for the JJammu Express to cross Jai completely.

Explanation:

The speed of Jammu Express is given to be $20{km}/{h}$.

In SI units,

$20km/h=\dfrac{20\times 1000}{60\times 60} \dfrac{m}{s}=\dfrac{100}{18}\dfrac{m}{s}\end{aligned}$.

Jai is moving in the opposite direction of the train at $\dfrac{5}{18}\dfrac{m}{s}$.

Since the jammu Express and Jai's car are moving in opposite directions, their individual speeds add up to form the relative velocity $v_r$ given by

$v_r = v_{train} + v_{Jai}\\\\= \dfrac{100}{18}\dfrac{m}{s} + \dfrac{5}{18}\dfrac{m}{s}\\\\=\dfrac{105}{18}\dfrac{m}{s}.$

Now, for the Jammu express to cross Jai completely, a distance of 700 m has to cross Jai.

Since we know $Speed = \dfrac{distance}{time},$ we can write $time = \dfrac{distance}{speed}$.

Therefore,

$time = \dfrac{700}{\dfrac{105}{18}} s\\\\\\= \dfrac{700 \times18}{105} s\\\\= 120 s$