# RRB NTPC - Problems on Trains

1.

A boat is rowed down a river 40 km in 5 hr and up a river 21 km in 7 hr. Find the speed of the boat and the river.

A.) 61/12 kmph
B.) 4.5 kmph
C.) 5 kmph
D.) 5.5 kmph

Speed of the boat downstream = 40/5 = 8 kmph
Speed of the boat upstream = 21/7 = 3 kmph
Speed of the boat = 1/2 ( 8+3) = 11/2 = 5.5 kmph

2.

A train 280 m long, running with a speed of 63 km/hr will pass a tree in:

A.) 15 seconds
B.) 20 seconds
C.) 16 seconds
D.) 18 seconds

Given
Length of the train = 280 m
Speed of the train = 63 km / hr
---> To convertkm/hr to m/sec multiply speed with (5 / 18)
= 63 x (5 / 18) m/sec
= 17.5 m/sec
ThereforeSpeed of the train =17.5m/sec
Now,Time taken by the train tocross an electric pole =Length of the train/Speed of the train
= 280/17.5
16 sec
The time taken is16 sec.

3.

A train 800 m long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 minute, then the length of the tunnel is:

A.) 540 m
B.) 130 m
C.) 500 m
D.) 260 m

Given, Length of the train = 800 m
Speed of the train = 78 km/hr (convert km/hr to m/sec)
= 78 × (5/18) m /sec
= 21.667 m /sec
=> Speed of the train = 21.667 m /sec
Time taken by the train to cross the tunnel = 1 min = 60 sec
To find the length of the tunnel:
Time taken by train to cross tunnel = (Length of tunnel + Length of train) / speed of the train
=> 60 = (Length of tunnel + 800) / 21.667
=> 60 × 21.667 = Length of tunnel + 800
=> 1300 = Length of tunnel + 800
=> 1300 – 800 = Length of tunnel
=> 500 = Length of tunnel
Thus, the Length of tunnel = 500 m

4.

A train running at the speed of 60 km/hr crosses a pole in 9 seconds. What is the length of the train?

A.) 150 m
B.) 160 m
C.) 240 m
D.) 250 m

Speed = 60 x 5/18 m/sec = 50/3 m/sec.
Length of the train = (Speed x Time) = 50/3 x 9 m = 150 m.

5.

A 240m long train is running at 90kmph. If it crossed the platform in 30sec, then find the length of the platform?

A.) 490m
B.) 500m
C.) 510m
D.) 550m