SOLUTION: A rock is thrown upward with a velocity of 25 meters per second from the top of a 20 meter high cliff, and it misses the cliff on the way back down. When will the rock be 7 meters
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Question 1099275: A rock is thrown upward with a velocity of 25 meters per second from the top of a 20 meter high cliff, and it misses the cliff on the way back down. When will the rock be 7 meters from the water, below? Round your answer to two decimal places Found 2 solutions by josmiceli, Boreal:Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
When will the height of the rock be ?
Use the quadratic formula ( use negative square root to get positive time ) sec
The rock will be 7 meters from the water in 5.58 sec
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check answer:
I think error is due to rounding off.
check the math & get another opinion if needed
You can put this solution on YOUR website! the equation is h(t)=-4.9t^2+25t+20
That equals 7 when the rock is 7 meters above the water.
Therefore -4.9t^2+25t+13=0=4.9 t^2-25t-13
t=(1/9.8)(25+/- sqrt (625+254.8); sqrt term is 29.66
t=54.66/9.8=5.58 sec.
