Acar speeds past you sounding its horn at a frequency of 1000hz. the frequency you hear:

f' =1064.1025 Hz

Explanation:

We know that from doppler's effect

f'= observed frequency

f= actual frequency =1000 Hz

v= velocity of sound waves = 332 m/s

v_o= velocity of observer =0

v_s= velocity of source. ( let velocity of car be 20 m/s)

therefore,

f' =1064.1025 Hz

in most common fires, oxygen is needed for an oxidation reaction to takes place. the combination of oxygen with any element as fuel can create fire and combustion will occur especially if wood, light materials and other combustible things are combine with oxygen.