A train running with 72km/hr takes 20sec to cross a platform 200 m lon...
200+L = 72*(5/18)*20. L= 200m.
400 + 200 = 72*(5/18)*t. So, t = 30sec
View all questions of this test
A train running with 72km/hr takes 20sec to cross a platform 200 m lon...
Given:
Speed of train (s) = 72 km/hr
Length of platform (l) = 200 m
To find:
Time taken to cross a stationary train having twice the length of the platform.
Solution:
1. First, let's convert the speed of the train from km/hr to m/s.
We know that,
1 km/hr = 5/18 m/s
Therefore, speed of the train (s) = 72 × 5/18 = 20 m/s
2. Now, let's find the time taken by the train to cross the platform.
We know that,
Speed = Distance/Time
Therefore, Time taken to cross the platform = Distance/Speed
Time taken to cross the platform = 200/20 = 10 seconds
3. Let's find the length of the stationary train.
We know that,
Time taken to cross a stationary object = Length of train + Length of platform / Speed
Therefore, Length of stationary train = Speed × Time taken to cross a stationary object - Length of platform
Length of stationary train = 20 × (10 + 20) - 200
Length of stationary train = 400 m
4. Now, let's find the time taken by the train to cross the stationary train.
We know that,
Time taken to cross a stationary object = Length of train + Length of platform / Speed
Therefore, Time taken to cross the stationary train = (2 × 200 + 400) / 20
Time taken to cross the stationary train = 30 seconds
Hence, the correct answer is option (b) 30 seconds.