An engine approaches a hill with a constant speed. When it is at a distance of 0.9 km it blows a whistle, whose echo is heard by the driver after 5 s. if the speed of sound in air is 330 m/s, the speed of engine is

Options

A. 10 m/s
B. 20 m/s
C. 30 m/s
D. 40 m/s

Answer

C

Explanation

`(900+900-ut)/(v)=t,1800=(u+v)t=(u+330)xx5," "u=30m//s`