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View all1The principle used in radar is the same as that of Sonar. In radar we use radio waves ; whereas in sonar we use ?2A body can escape the gravitational pull of the earth if it is thrown up with a velocity of?3The cracking sound heard when dry hair is combed with a hard rubber comb is due to_________?4The approximate intensity level of the sound which can cause damage to the ear drum is?5The waves which are used for line of sight (LOS) communication are called:6The Largest Producer of Electricity in the Islamic World is______________________?
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Correct Answer: C: 56 ft
Explanation: The correct answer is C: 56 ft. A distinct echo is heard only if the reflecting surface is at least 56 feet from the source of sound at ordinary temperatures. This minimum distance ensures the reflected sound reaches the ear at least 1/10th of a second after the original.