(i) A straight railway track is at a distance ‘d’ from you. A distant train approaches you travelling at a speed `u (lt` speed of sound`)` and crosses you. How does the apparent frequency `(f)` of the whistle change with time (`f_(0)` is the original frequency of the whistle). Draw a rough `f` vs `t` graph.
(ii) A bat is tracking a bug. It emits a sound, which reflects off the bug. The bat hears the echo of the sound `0.1` seconds after it originally emitted it. The bat can tell if the insect is to the right or left by comparing when the sound reaches its right ear to when the sound reaches its left ear. Bat’s ears are only `2 cm` apart. Bats also use the frequency change of the sound echo to determine the flight direction of the bug. While hovering in the air (not moving), the bat emits a sound of `40.0 kHz`. The frequency of the echo is `40.4 kHz`. Assume that the speed of sound is `340 m//s`.
(a) How far away is the bug?
(b) How much time delay is there between the echo reaching the two ears if the bug is directly to the right of the bat?
(c) What is the speed of the bug?

Answer

(i) `(##IJA_PHY_V01_C13_E01_079_A01##)`
(ii) (a) 17 m
(b) `5.9 xx10^(-5) s`
(c) `1.7 m//s`