Question:

An engine approaches a hill with a constant speed. When it is at a distance of 0.9km0.9\, km, it blows a whistle whose echo is heard by the driver after 55 seconds. If the speed of sound in air is 330m/s330\, m/s, then the speed of the engine is :

Updated On: Sep 27, 2024
  • 32 m/s
  • 27.5 m/s
  • 60 m/s
  • 30 m/s
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The Correct Option is D

Solution and Explanation

Let after 5 sec engine at point C
t=AB330+BC330t = \frac{AB}{330}+\frac{BC}{330}
5=0.9×1000330+BC3305 = \frac{0.9\times1000}{330}+\frac{BC}{330}
BC=750m\therefore BC=750\,m
Distance travelled by engine in 5\, sec
=900m750m=150m= 900\,m-750\,m= 150\,m
Therefore velocity of engine
=150m5sec=30m/s= \frac{150m}{5sec} = 30 \,m/s
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Concepts Used:

Waves

Waves are a disturbance through which the energy travels from one point to another. Most acquainted are surface waves that tour on the water, but sound, mild, and the movement of subatomic particles all exhibit wavelike properties. inside the most effective waves, the disturbance oscillates periodically (see periodic movement) with a set frequency and wavelength.

Types of Waves:

Transverse Waves -

Waves in which the medium moves at right angles to the direction of the wave.

Examples of transverse waves:

  • Water waves (ripples of gravity waves, not sound through water)
  • Light waves
  • S-wave earthquake waves
  • Stringed instruments
  • Torsion wave

The high point of a transverse wave is a crest. The low part is a trough.

Longitudinal Wave -

A longitudinal wave has the movement of the particles in the medium in the same dimension as the direction of movement of the wave.

Examples of longitudinal waves:

  • Sound waves
  • P-type earthquake waves
  • Compression wave