Most Important Selected Qs for JEE AdvancedPhysicsWaves and Sound
A car moves towards a hill with speed v₀ . It blows a horn of frequency f which is heard by an observer following the car with speed v ₀ . The speed of sound in air is v .
Options
- AThe wavelength of sound reaching the hill is v f
- BThe wavelength of sound reaching the hill is v-v_c f
- CThe wavelength of sound of horn directly reaching the observer is v+v_c f
- DThe beat frequency observed by the observer is 2 v_c (v+v₀ ) f v^2-v_c^2
Correct answer
D. The beat frequency observed by the observer is 2 v_c (v+v₀ ) f v^2-v_c^2
Step-by-step solution
Frequency of horn directly heard by observer v+v₀ v+v_c f Frequency of echo = v v+v_c f Frequency of echo of horn as heard by observer. v v-v_c f ( v+v₀ v ) Frquency of Beats : = (v+v₀ ) f 1 v-v_c - 1 v+v_c = 2 v_c (v+v₀ ) (v^2-v_c^2 ) f