A train crosses a platform in 30 s travelling with a speed of 48 km/h. If the length of the train be 200 m, then the length of the platform is
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two objects are moving in opposite directions towards each other at speeds u and v, then relative speed = Speed of first + Speed of second = u + v.
This is also the speed at which they are moving towards each other or the speed at which they may be moving away from each other.
2. If the two objects move in the same direction with speeds u and v, then
relative speed = difference of their speeds = u – v.
This is also the speed at which the faster object is either drawing closer to the slower object or moving away from the slower object as the case may be.
Important Models:
Model 1. 1 Pole and I Train:
Length of The Train (m) = Speed of the Train (m/s) × Time taken to cross the pole (s)
Model 2. 1 Train and 1 Platform:
Length of the Train + Length of the Platform (m) = Speed of the Train (m/s) × Time taken to cross the platform (s)
Model 3. 1 Train with speed speed v1 and 1 moving person with speed v2
Case 1: If both are moving in same direction
Length of The Train (m) = [Speed of the Train - Speed of the Man] (m/s) × Time taken to cross the man (s)
Case 2: If both are moving in opposite direction
Length of The Train (m) = [Speed of the Train + Speed of the Man] (m/s) × Time taken to cross the man (s)
Model 4. 2 Trains with speeds v1,v2
Case 1: If both are moving in same direction
[Length of The Train 1 + Length of the Train 2](m) = [Speed of the Train1 - Speed of the Train 2] (m/s) × Time taken to cross (s)
Case 2: If both are moving in opposite direction
[Length of The Train 1 + Length of the Train 2](m) = [Speed of the Train1 + Speed of the Train 2] (m/s) × Time taken to cross (s)
1. A train running at certain speed crosses a stationary engine in 20 seconds. To find out the speed of the train, which of the following information is necessary:
a. Only the length of the train
b. Only the length of the engine
c. Either the length of the train or the length of the engine.
d. Both the length of the train and the length of the engine.
Correct Option : D
Explanation:
Since the sum of the length of the train and the length of the engine is needed, so both the lengths must be known.
This is also the speed at which they are moving towards each other or the speed at which they may be moving away from each other.
2. If the two objects move in the same direction with speeds u and v, then
relative speed = difference of their speeds = u – v.
This is also the speed at which the faster object is either drawing closer to the slower object or moving away from the slower object as the case may be.
Important Models:
Model 1. 1 Pole and I Train:
Length of The Train (m) = Speed of the Train (m/s) × Time taken to cross the pole (s)
Model 2. 1 Train and 1 Platform:
Length of the Train + Length of the Platform (m) = Speed of the Train (m/s) × Time taken to cross the platform (s)
Model 3. 1 Train with speed speed v1 and 1 moving person with speed v2
Case 1: If both are moving in same direction
Length of The Train (m) = [Speed of the Train - Speed of the Man] (m/s) × Time taken to cross the man (s)
Case 2: If both are moving in opposite direction
Length of The Train (m) = [Speed of the Train + Speed of the Man] (m/s) × Time taken to cross the man (s)
Model 4. 2 Trains with speeds v1,v2
Case 1: If both are moving in same direction
[Length of The Train 1 + Length of the Train 2](m) = [Speed of the Train1 - Speed of the Train 2] (m/s) × Time taken to cross (s)
Case 2: If both are moving in opposite direction
[Length of The Train 1 + Length of the Train 2](m) = [Speed of the Train1 + Speed of the Train 2] (m/s) × Time taken to cross (s)
1. A train running at certain speed crosses a stationary engine in 20 seconds. To find out the speed of the train, which of the following information is necessary:
a. Only the length of the train
b. Only the length of the engine
c. Either the length of the train or the length of the engine.
d. Both the length of the train and the length of the engine.
Correct Option : D
Explanation:
Since the sum of the length of the train and the length of the engine is needed, so both the lengths must be known.
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