An engine approaches a hill with constant speed and where it is at a distance of 1 km blows a whistle whose echo is heard by the driver 5s. If the speed of the sound is `340 ms^(-1)`. The speed of the engine is

Options

A. `60 ms^(-1)`
B. `172 ms^(-1)`
C. `340 ms^(-1)`
D. `40 ms^(-1)`

Answer

A

Explanation

Speed of the railway engine is 'v'. The ditance covered by the engine in 5s in 5v.
The distance travelled by the sound in reaching the hill and coming back to the moving driver is , `= 1000 + (1000 -5v)= 2000 - 5v`
velocity of sound
`= ("distance travelled by sound")/("time")`
`V = (2000 - 5v)/(5)`
`340 xx 5 = 2000 - 5v`
`1700 = 2000 -5v`
`-300 = -5v`
`v = (300)/(5) = 60 m//s`