Because of the doppler effect, the sound heard by an observer listening to a moving ambulance siren, compared to what the observer would have heard if the observer and siren were both at

a. will have a lower frequency if the ambulance siren is moving towards the observer
b. will have a higher frequency if the ambulance siren is moving away from the observer.
c. will have a higher frequency if the ambulance siren is moving towards the observer.
d. will have a lower pitch if the ambulance siren is moving towards the observer.
e. will have a longer wavelength if the ambulance siren is moving towards the observer.

C. will have a higher frequency if the ambulance siren is moving towards the observer.

Explanation:

A) it is wrong

Source moving towards the observer, observer will listen higher frequency.

B) Again wrong

Source is moving away from observer, observer will hear lower frequency.

C) correct.

will have a higher frequency if the ambulance siren is moving towards the observer

D) Wrong as pitch is equivalent to frequency

Source moving towards the observer, observer will listen higher pitch.

E)  wrong

will have shorter wavelength because the frequency increases.

only C is correct.

find the sum of the two horizontal vectors and the sum of the two vertical vectors

isoceles right angled triangle