Question

A bat, flying toward the east at 2.0 m/s, emits a shriek that is reflected back to it from a wall that is 20.0 m in front of the bat at the instant the shriek is emitted. Sound travels at 340 m/s in the air. How many milliseconds after emitting the shriek does the bat hear the reflected echo from the wall?

Answer 1

Answer:

The bat hear the reflected echo after 117.6 s after emitting the shriek.

Explanation:

Given:

• Distance between the wall and the bat d=20 m

• speed of sound in air v=340 m/s

It is given that the shriek is reflected back at the same instant it is emitted.

So the total distance travelled sound in air is 2d =40 m.

The time taken in reaching to the wall and coming back to the bat is same.

Let t be the time taken given by

$t=\dfrac{2d}{v}\\t=\dfrac{40}{340}\\t=1.176\ \rm s\\t=117.6\ \rm milliseconds$

Answer 2

Answer:

$T = 116.9 ms$

Explanation:

As we know that bat emits the sound when it was at distance of 20.0 m from the wall

so the time taken by the sound to reach the wall is given as

$t_1 = \frac{20}{340}$

$t_1 = 58.8 ms$

Now in the same time distance moved by bat is

$d_1 = v t$

$d_1 = 0.1176 m$

now distance between bat and the wall is given as

$d' = 20 - 0.1176 = 19.88 m$

now since reflected sound and bat both moving towards each other so here time taken to reach the sound again on bat is given as

$t_2 = \frac{d'}{v + v_s}$

$t_2 = \frac{19.88}{340 + 2}$

$t_2 = 58.1 ms$

so total time taken is given as

$T = 58.1 + 58.8$

$T = 116.9 ms$