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21. A body thrown vertically up from ground passes theheight of 25 m twice in an interval of 4 sec. Theinitial velocity of body is -(A) 30 ms-1(B) 20 ms!(C) 50 ms 1(D) 40 ms-1 |
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Answer» (A) - 30 m/sExplanation:LETS assume the initial velocity to be u.s = 25, u =u, a = -gv² - u² = 2as v² = u² - 50G -------- (1)After 25 m is crossed, the TIME of flight to return BACK to the same point is T = 2v/g 4 = 2v/10 , v = 20Substitute v in equation 120² = u² - 50(10) 900 = u² u = 30 |
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