Arjun is standing on an old
building and there is a railway track beside, on which a train travels at a speed of 72 kmph. When the train passes by the building, Arjun tries to jump inside the train. He somehow manages to enter the train through the last door of the last bogie. After jumping in, he runs towards the other end of the train at a speed of 36 kmph. When he reaches a distance of 300 m from the building the building exploded. After how many seconds since Arjun's jump did the building explode?
a.30s. b.10s c.15s d.20s
Answers
Answer:
A train running at the speed of 60 km/hr. It crosses a certain pole that is in the way in 9 seconds. What is the length of the train?
A) 200 meters B) 180 meters C) 376 meters D) 150 meters
Answer: The train crosses the pole in 9 seconds. This means that from the point when the engine or the front of the train crosses the pole to the point when the back of the train reaches the pole, we have 9 seconds. Thus we can get the length of the train by calculating the distance that the train travels in 9 seconds.
We have the speed of the train = 60 km/hr. We have to convert it into m/s. Let us see the trick to convert km/hr to m/s:
1km/1h = 1×(1000/60×60) = 1×(5/18) m/s.
Therefore if the speed is ‘x’ km/hr then we can change it to m/s by multiplying x with 5/18. Let us do it for the current example.
We have the speed of the train = 60 km/hr or 60×(5/18) = 50/3 m/s.
Therefore in 9 seconds, the train will cover a distance = speed×time
In other words, we have the Distance = (50/3 m/s)×9 = 150 m. Therefore the correct option is D) 150 meters. Let us see some more examples that can be formulated on the basis of this concept.
Answer:
10s
Step-by-step explanation:
72kmph = 20m/s
36kmph = 10m/s
Relative speed = (20+10)m/s = 30m/s
Given distance travelled = 300m
so, time taken = distance/speed
= (300/30)s
= 10s