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A rock is thrown upward with a velocity of 26 meters per second from the top of a 43 meter high cliff, and it misses the cliff on the way back down. When will the rock be 6 meters

Answer :

After 5.98 seconds the rock reaches 6 meter

Explanation:

We need to find when will the rock be 6 meters,

That is displacement = 6 - 26 = -20 m

We have equation of motion s = ut + 0.5 at²

        Initial velocity, u = 26 m/s

        Acceleration, a = -9.81 m/s²  

        Displacement, s = -20 m      

     Substituting

                      s = ut + 0.5 at²

                      -20 = 26 x t + 0.5 x -9.81 x t²

                      4.905 t²  - 26 t -20 = 0

                      t = 5.98 s    or   t = -0.68 s

Time is always positive,

So after 5.98 seconds the rock reaches 6 meter

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