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JEE Main 2019 (12 Jan, Shift 1) · Relative Velocity in Two Dimensions

Relative Velocity in Two Dimensions question from JEE Main 2019 (12 Jan, Shift 1)

Q20JEE Main 2019 · 12 JAN · SHIFT 1Medium

Relative Velocity in Two Dimensions

A person standing on an open ground hears the sound of a jet aeroplane, coming from north at an angle 60o with ground level. But he finds the aeroplane right vertically above his position. If v is the speed of sound, speed of the plane is:

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Answer: (d)

  1. Sound travels from the old position along a line at 60∘60^\circ to the ground, distance vtvt.
  2. In the same time the plane moves horizontally to directly overhead: vpt=vtcos⁡60∘v_p t = vt\cos 60^\circ
  3. vp=v2v_p = \frac{v}{2}
  4. So the answer is (d).
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