# How many seconds must a passenger count clicks to equal the exact speed of the train, in kilometres per hour?

While riding on a train you can hear the click of the wheels passing over the joins in the rails. If each rail is 10m long, how many seconds must a passenger count clicks to equal the exact speed of the train, in kilometres per hour?

### 2 Answers

- billrussell42Lv 77 years agoFavorite Answer
let V be speed in km/hour. 1000V is m/hour and (1000/3600)V is m/s or 10/36 or (5/18)V.

At that speed, with one click = 10 m, we get

(5/18)V m/s x (1click/10m) = (5/180) click/s = (1/36) clicks/s

Now we get to the problem:

"how many seconds must a passenger count clicks to equal the exact speed of the train" ?? this doesn't make sense. how can seconds equal the speed?

One guess is that the NUMBER of seconds between clicks numerically equals the speed in km/hr?

(1/36) clicks/s

inverting this, we get 36 seconds per click

V = 36 seconds

- IanLv 77 years ago
Since each click is 10m, and 1km = 1,000m, 1km is equivalent to 100 clicks.

Thus a speed of x km/hr is equivalent to 100x clicks per hour, or x clicks per 1/100 of an hour.

An hour is 60*60 = 3600 seconds, so 1/100 of an hour is 36 seconds. Therefore x km/hr is equivalent to x clicks per 36 seconds.

So the number of clicks counted for 36 seconds equals the speed in kilometers per hour.

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