Whistle moving toward wall produces 11 beats/s with reflection

[05holtel]

Homework Statement

You blow a whistle of frequency 769 Hz, as you move towards a wall.

The frequency of beats you hear from the whistle and the reflected sound is 11 beats/s.

How fast are you moving towards the wall?

Give your answer in m/s and to two significant figures.

Only answer in numerical values, no units.

Homework Equations

The Attempt at a Solution

769 + 11 = 780hz. Which I believe is the new frequency

Now what?
Thanks in advance

 

[Gear300]

You should use the Doppler Effect.

 

[05holtel]

Thanks I got it