InterviewSolution
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InterviewSolution
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A stone is thrown vertically up from the tower of height 25m with a speed of 20 m/s What time does it take to reach the ground ? (g=10 m//s^(2)) |
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Answer» Solution :Sign convention must be used to solve this problem. It is shown in figure. We consider the upward direction as positive and DOWNWARD direction as NEGATIVE with respect to a point of reference. In the above example the point of projection is considered as the point of reference. Then, u=20 m/s `a=g=-10 m//s^(2)` `s=h=-25 m` From equation of motion `s=ut + 1//2 at^(2)` `-25 =20 t-1//2 X 10 x t^(2)` `-25=20t -5 t^(2)` `-5=4t -t^(2)` `rArr t^(2)-4t-5=0` Solving this equation, We get, (t-5) (t+1)=0 t=5 or -1 t=5s |
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