Question : What is the minimum distance (in metres) required to hear an echo?
Option 1: 10
Option 2: 13
Option 3: 17
Option 4: 21
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Correct Answer: 17
Solution : The correct option is 17
The sound wave must reach the surface and return in a time interval that our ears can distinguish as different sounds in order for us to detect a distinct echo. Since the sound needs to travel to the surface and back, essentially covering twice the distance, the minimum distance for a detectable echo is often around 17 meters.
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Question : The upper part of a tree broken at a certain height makes an angle of 60° with the ground at a distance of 10 metres from its foot. The original height of the tree was:
Option 1: $20\sqrt{3}$ metres
Option 2: $10{\sqrt3}$ metres
Option 3: $10\left (2+{\sqrt3} \right)$ metres
Option 4: $10\left (2-{\sqrt3}\right)$ metres
Question : Sound travels 330 metres in a second. When the sound follows the flash of lightning after 10 seconds, the thundercloud will be at a distance of:
Option 1: 1300 metres
Option 2: 2000 metres
Option 3: 3650 metres
Option 4: 3300 metres
Question : The shadow of a tower when the angle of elevation of the sun is 45°, is found to be 10 metres longer than when it was 60°. The height of the tower is:
Option 1: $5\sqrt{3}-1$ metres
Option 2: $5(3+\sqrt{3})$ metres
Option 3: $10(\sqrt{3}-1)$ metres
Option 4: $10(\sqrt{3}+1)$ metres
Question : A boat running upstream takes 10 hours to cover a certain distance, while it takes 7 hours to cover the same distance running downstream. What is the ratio between the speed of the boat and that of the water current, respectively?
Option 1: 17 : 5
Option 2: 3 : 17
Option 3: 2 : 17
Option 4: 17 : 3
Question : The top of a broken tree touches the ground at a distance of 15 metres from its base. If the tree is broken at a height of 8 metres from the ground, then the actual height of the tree is:
Option 1: 17 metres
Option 2: 20 metres
Option 3: 25 metres
Option 4: 30 metres
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