A train approaching a hill at a speed 40 km h - 1 sounds a whistle of frequency 580 Hz when it is a distance of 1 km from the hill. A wind with speed 40 km h - 1 is blowing in the direction of motion of the train. (Velocity of sound in air = 1200 km h - 1 ) The frequency of echo is

Question

A train approaching a hill at a speed 40 km h - 1 sounds a whistle of frequency 580 Hz when it is a distance of 1 km from the hill. A wind with speed 40 km h - 1 is blowing in the direction of motion of the train. (Velocity of sound in air = 1200 km h - 1 ) The frequency of echo is, 599 Hz, 590 Hz, 610 Hz, 620 Hz

MARKS App · Accepted Answer

f hill = f v + v m + v 0 v - v m - v s = 580 1200 + 40 + 0 1200 + 40 - 40 = 580 × 1240 1200 f e c h o = f hill v - v m + v 0 v - v m Here f hill is the frequency that incidents on the hill = 580 × 1240 1200 1200 - 40 + 40 1200 - 40 = 580 × 1240 1200 × 1200 1160 = 620 H z

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