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  • By which velocity a ball be projected vertically downward so that the distance covered by it in 5th second is twice the distance it covers in its 6th second ( g= 10 m / s2 ) &nbsp

By which velocity a ball be projected vertically downward so that the distance covered by it in 5th second is twice the distance it covers in its 6th second ( g= 10 m / s2 )
 

Option: 1

13 m/s


Option: 2

65 m/s


Option: 3

63 m/s

 


Option: 4

68 m/s


Answers (1)

best_answer

 

       If a body is projected vertically downward with some initial velocity

                   \begin{array}{l}{\text { Equation of motion: } \quad v=u+g t} \\ {\qquad \begin{array}{ll}{h=} & {u t+\frac{1}{2} g t^{2}} \\ {v^{2}} & {=u^{2}+2 g h} \\ {h_{n}} & {=u+\frac{g}{2}(2 n-1)}\end{array}}\end{array}

        

\begin{array}{l}{\text { By formula } h_{n}=u+\frac{1}{2} g(2 n-1) \Rightarrow u-\frac{10}{2}[2 \times 5-1]=2\left\{u-\frac{10}{2}[2 \times 6-1]\right\}} \\ {\Rightarrow u-45=2 \times(u-55) \Rightarrow u=65 \mathrm{m} / \mathrm{s}}\end{array}

Posted by

Ritika Kankaria

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