Question

A 100 m long train is moving at a speed of 60 km/h.in what time wil it cross a sign pole?

Answer 1

speed=60kmph=60×5/18mps=50/3mps
distance=200m speed=distance /time

Answer 2

Heya

∆ Just ended up reading about inertial frames and stuff so, I'll try explaining what exactly the Question wants you to do !

1 ) The train is 100m

2 ) The Train is at *Rest*

3 ) The velocity of Pole is *60 kmph*

Now, how can the pole move !!

Pretty simple, for an observer sitting inside the Train, the Train Itself is at rest ! that is, when we're inside the Train, and take the Train as the Frame of Reference, we assume all the stationary objects as *Moving* except us ✓✓

Now, back to original sum.

Clearly, the Pole has to travel 100m and has a velocity, i.e, the rate of change of *POSITION* is 60kmph ✓✓

Hence, by s = ut, we have :

∆ Time taken to cross the train completely is :
$\frac{100m}{60kmph}$

∆ Using the Preferred Units, we have :
$t = \frac{0.1}{60} h$

∆ An hour is 3600 seconds

Hence,
$t = 6s$

Therefore, the time taken by the Pole to overtake the Train( rest ) is : 6 seconds

∆ Now, considering the inertial frame of reference, i.e, the Earth/ the Ground,

We can say that the Train might take 6 seconds to cross that Pole if traveling with that constant velocity of 60 kmph ✓✓