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A ball is thrown vertically upwards. It was observed at a height h twice with a time interval increment t. The initial velocity of the ball is

  1. square root of 8 g h plus g to the power of 2 end exponent open parentheses increment t close parentheses to the power of 2 end exponent end root  
  2. square root of 8 g h plus open parentheses fraction numerator g increment t over denominator 2 end fraction close parentheses to the power of 2 end exponent end root  
  3. fraction numerator 1 over denominator 2 end fraction square root of 8 g h plus g to the power of 2 end exponent open parentheses increment t close parentheses to the power of 2 end exponent end root  
  4. square root of 8 g h plus 4 g to the power of 2 end exponent open parentheses increment t close parentheses to the power of 2 end exponent end root  

The correct answer is: fraction numerator 1 over denominator 2 end fraction square root of 8 g h plus g to the power of 2 end exponent open parentheses increment t close parentheses to the power of 2 end exponent end root


    Let the ball be at height h at time t and time open parentheses t plus increment t close parentheses.
    Then,
    h equals u t minus fraction numerator 1 over denominator 2 end fraction g t to the power of 2 end exponent(i)
    and h equals u open parentheses t plus increment t close parentheses minus fraction numerator 1 over denominator 2 end fraction g open parentheses t minus increment t close parentheses to the power of 2 end exponent(ii)
    Equating Eqs. (i) and (ii), we get
    t equals fraction numerator 2 u minus g increment t over denominator 2 g end fraction (iii)
    Substituting Eq. (iii) in Eq. (i), we get
    h equals fraction numerator 4 u to the power of 2 end exponent minus g to the power of 2 end exponent open parentheses increment t close parentheses to the power of 2 end exponent over denominator 8 g end fraction
    rightwards double arrow blank u equals fraction numerator 1 over denominator 2 end fraction square root of 8 g h plus g to the power of 2 end exponent open parentheses increment t close parentheses to the power of 2 end exponent end root

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