| A train overtakes two persons walking along a railway track. The first one walks at 4.5 km/h and the other one walks at 5.4 km/h. The train needs 8.4 s and 8.5 s, respectively to overtake them. What is the speed of the train, if both the persons are walking in the same direction as the train? |
A) 66 km/h
B) 72 km/h
C) 78 km/h
D) 81 km/h
E) None of these
Correct Answer: D
Solution :
| Speed of Ist person km/h \[=\left( 4.5\times \frac{5}{18} \right)m/s\] |
| \[=\frac{5}{4}m/s=1.25\,m/s\] |
| Speed of IInd person = 5.4 km /h |
| \[=\left( 5.4\times \frac{5}{18} \right)m/s=\frac{3}{2}m/s=1.5\,m/s\] |
| Let the speed of the train be x m/s. |
| Then, \[(x-1.25)\times 8.4=(x-1.5)\times 8.5\] |
| \[\Rightarrow \] \[8.4x-10.5=8.5x-12.75\] |
| \[\Rightarrow \] \[0.1x=2.25\]\[\Rightarrow \]\[x=22.5\] |
| \[\therefore \]Speed of the train \[=\left( 22.5\times \frac{18}{5} \right)=81\,\,km/h\] |
You need to login to perform this action.
You will be redirected in
3 sec
