| A train 140 m long passes a man, running at 6 km/h in the direction opposite to that of the train in 9 s. The speed of the train is |
A) 50 km/h
B) 45 km/h
C) 42 km/h
D) 40 km/h
Correct Answer: A
Solution :
| Let the speed of the train be x km/h. Then, relative |
| speed \[=(x+6)km/h=\frac{5\,\,(x+6)}{18}m/s\] |
| \[\text{Relative}\,\,\text{speed}=\frac{\text{Length}\,\,\text{of}\,\,\text{train}}{\text{Time}\,\,\text{taken}\,\,\text{to}\,\,\text{cross}\,\,\text{each}\,\,\text{other}}\]\[\Rightarrow \]\[\frac{5\,\,(x+6)}{18}=\frac{140}{9}\]\[\Rightarrow \]\[x+6=\frac{2\times 140}{5}\] |
| \[x=50\,\,km/h\] |
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