When the train passes through a bridge or platform or tunnel or a stationary object having some length

If length of train = x meters and length of the stationery object = y meters.

Also, speed of the train is z km/hr, then time taken by the train to pass the stationary object having length y meters.

= (length of the train + length of stationary object)/speed of the train

= (x meters + y meters)/z km/hr

**Note:** Change km/hr to m/sec.

Solved examples to calculate when the train passes through a bridge or a stationary object having some length.

**1.** A train 175 m
long crosses a bridge which is 125 m long in 80 seconds. What is the speed of
the train?

**Solution: **

Length of the train = 175 m.

Length of the bridge = 225 m

Distance covered by the train to cross the bridge = (175 + 225) m

= 400 m

Time taken by the train to cross the bridge = 80 seconds

Speed = distance/time

= 400/80 m/sec

= 5 m/sec.

**2.** A train 220 m
long is running at a speed of 36 km/hr. What time will it take to cross a 110 m
long tunnel?

**Solution: **

Length of the train = 220 m

Length of the tunnel = 110 m

Therefore, length of the train + length of the tunnel = (220 + 110) m = 330m

Speed of the train = 36 km/hr

Speed of the train = 36 × 5/18 m/sec = 10 m/sec

Therefore, time taken by the train to cross the tunnel = 330 m/10 m/sec.

= 33 seconds.

**3.** Find the time
taken by 150 m long train passes through a bridge which is 100 m long, running
at a speed of 72 km/hr.

**Solution:**

Speed of train = 72 km/hr = 72 × 5/18 m/sec = 20 m/sec

In order to cross a bridge of length 100 m, the train will have to cover a distance = (150 + 100) m = 250 m

Thus, speed = 20 m/sec and distance = 250 m

Time = distance/speed

= 250m/20 m/sec

= 25/2 sec

= 12.5 sec.

**4.** A 90 m long
train is running at a speed of 54 km/hr. If it takes 30 seconds to cross a
platform, find the length of the platform.

**Solution: **

Speed of the train = 54 km/hr = 54 × 5/18 m/sec = 15 m/sec

Time taken to cross the bridge = 30 sec

Distance covered by train to cross the platform = speed × time

= (15 × 30) m

= 450 m

To cross the platform, train covers a distance = length of train + length of platform

450 m = 90 m + length of platform

Therefore, length of platform = (450 – 90) m = 360 m

**Relationship between Speed, Distance and Time**

**Problems on Calculating Distance**

**Two Objects Move in Same Direction**

**Two Objects Move in Opposite Direction**

**Train Passes a Moving Object in the Same Direction**

**Train Passes a Moving Object in the Opposite Direction**

**Two Trains Passes in the Same Direction**

**Two Trains Passes in the Opposite Direction**

**8th Grade Math Practice**

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