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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 4 September 2020, Shift 2, Physics Q10

Question 10 of 75 in this shift, Physics question 10 of 25.

The driver of a bus approaching a big wall notices that the frequency of his bus's horn changes from 420 Hz to 490 Hz when he hears it after it gets reflected from the wall. Find the speed of the bus if speed of the sound is 330 ms−1^{-1}.
  1. (1)71 kmh−1^{-1}
  2. (2)81 kmh−1^{-1}
  3. (3)91 kmh−1^{-1}Official answer
  4. (4)61 kmh−1^{-1}

Official answer

Option 3

NTA final key (Sep 2020).

Chapter
Waves
Topic
Doppler Effect
Idea tested
Moving Reflector Echo

Same idea in other shifts

Asked 3× in all
  1. 6 Apr 2023, Shift 1 · Q51A person driving car at a constant speed of 15 m/s is approaching a vertical wall. The person notices a change of 40 Hz in the frequency…MediumNumerical value
  2. 28 Jul 2022, Shift 1 · Q57The frequency of echo will be __________ Hz if the train blowing a whistle of frequency 320 Hz is moving with a velocity of 36 km/h…MediumNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.