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

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