Important questions in Time and Distance for Police recruitment exam

Hyderabad: This article is in continuation to the last article on preparation for the Sub-Inspector of Police recruitment exam. Here are some practice questions and solutions on the Time and Distance topic.

TRAINS
It is a part of Time and Distance. The train-based questions depend on time, distance and speed. Before the question, first we will discuss basics in trains.

If a train has to cover a standing person or a tree or pole, then train has to cover its own length.
Here Distance = Length of the train

If a train has to cross a platform or a bridge, then train has to cover, the sum of lengths of train and platform or bridge.
Here Distance = Sum of lengths of train and platform or bridge

If two trains are running same direction, when they cross each and other, the distance and relative speeds are as follow:
Distance = Sum of lengths of two trains

Relative Speed = Difference between speeds of two trains

So, the time taken by the trains to cross each other = Distance/Speed

However, if two trains are running in opposite direction, when they cross each and other, the distance and relative speeds are as follow.

Distance = Sum of lengths of two trains
Relative Speed = Sum of speeds of two trains
So, the time taken by the trains to cross each other = Distance/Speed

Now we will discuss some examples

1. A train whose length is 360 meter is running at the rate of 72 km/hr. How long will it take to cross a standing person?

Solution:
Distance = Length of the train = 360 m
Speed = 72 km/hr

If distance is in metre, speed should be m/s, so convert speed from km/hr to m/s.
Speed = 72 × 5/18 = 20 m/s
Time = 360/20 = 18 sec

2. How long does a train 350 m long moving at the rate of 40 km/hr take to pass a bridge 250 m long?
Solution:
Distance = 350 250 = 600 m
Speed = 40 km/hr = 40 × 5/18 = 200/18 m/s
Time = 600 × 18/200 = 54 sec

3. A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. Then find the speed of the train?
Solution:
The train and a man are running same direction. Let’s say Speed of the Train is x km/hr
Relative Speed = (x – 5) km/hr = (125/10 × 18/5) km/hr
(x – 5) = 45
X = 50 km/hr

4. A 130 metres long train is running at 45 km/hr and cross a bridge in 30 seconds. Find the length of the bridge?
Solution:
Let length of the bridge is = x m
Speed = 45 km/hr = 45 × 5/18 = 25/2 m/s
Time = 30 seconds
Distance = (130 x) m
Then = (130 x)/30= 25/2
= 260 2x = 750
2x = 490
X = 245 m

Banda Ravipal Reddy
Director, SIGMA
Sai Institute of General Mental Ability
Hyderabad
Ph. 9491614131