A bat moving at 10 m/s towards a wall sends a sound signal of 8000 Hz towards it. On reflection it hears a sound of frequency f. The value of f in Hz is close to (speed of sound = 320 m/s)

The time taken relative to the bat for the sound wave to travel distance S between consecutive wavefronts traveling towards the wall is

T = S / (V_sound + V_bat) = 1 / 8000

Solving for S:

S = (V_sound + V_bat) / 8000 = (V_sound - V_bat) / f

After reflection, as the bat is moving towards the wall, the time taken by the sound to travel distance S is given as:

T' = S / (V_sound + V_bat)

Substituting the value of S from the previous equation into this one:

T' = (V_sound - V_bat) / (8000 * (V_sound + V_bat))

The apparent frequency will be:

f' = 1 / T'

f' = (V_sound + V_bat) / (V_sound - V_bat) * 8000

f' = (320 + 10) / (320 - 10) * 8000

f' = 330 / 310 * 8000

f' = 8516 Hz

Hence the correct answer is 8516 Hz.