A train is moving in an elliptical orbit in anticlockwise sense with a speed of `110(m)/(s)`. Guard is also moving in the given direction with same speed as that of train. The ratio of the length of major and minor axes is `(4)/(3)`. Driver blows a whistle of 1900 Hz at P, which is received by guard at S. The frequency received by guard is (velocity of sound `v=330(m)/(s)`)

Options

A. 1900 Hz
B. 1800 Hz
C. 2000 Hz
D. 1500 Hz

Answer

B

Explanation

Frequency received by guard is
`n_0=n_0(v_0(v+v_0costheta_1))/(v+v_Scostheta_2)`
`v=330(m)/(s)`
Here `v_0=v_S=(v)/(3)`,`costheta_1=(3)/(5)`,`costheta_2=(4)/(5)`.
`n=n_0((v+(v)/(3)xx(3)/(5)))/((v+(v)/(3)xx(4)/(5)))`
`=((6)/(5)xx(15)/(19))n_0=(18n_0)/(19)=1800Hz`