A train blowing its whistle moves with a constant velocity `v` away from an observer on the ground. The ratio of the natural frequency of the whistle to that measured by the observer is found to be `1.2`. If the train is not rest and the observer moves away from it at the same velocity, this ratio would be given by

Options

A. `0.51`
B. `1.25`
C. `1.52`
D. `2.05`

Answer

B

Explanation

`f_(1) = f_(0) (v_("sound"))/(v_("sound") + v_("train")) = (1)/(1.2)f_(0) rArr 1.2 v_("sound") = v_("sound") + v rArr v = (v_("sound"))/(5)`
`f_(2) = f_(0) (v_("sound") - v_("man"))/(v_("sound")) = 0.8 rArr (f_(0))/(f_(2)) = 1.25`