Question
From where do plants obtain hydrogen?
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An echo is returned in 6 seconds. What is the distance of reflecting surface from source? [given that speed of sound is 342m/ s.]
How many types of organisms are believed to be present on Earth?


A boy weighing 50kg climbs up a vertical height of 100m. Calculate the amount of work done by him. How much potential energy does he gain? (8 = 9.8m/s2).