SOLUTION: A stone is thrown upwards with an initial speed of 56 m/s. its height is h metres above the ground aft t seconds is given approximately by the formula h= 56t-5t^2. After how many s

Question 776285: A stone is thrown upwards with an initial speed of 56 m/s. its height is h metres above the ground aft t seconds is given approximately by the formula h= 56t-5t^2. After how many seconds will the stone be 50m above the ground? Explain.
Thats the question, i would truly appreciate it if someone would help me clarify this question... :)
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!

The first term, has nothing to do with gravity,
just the upward velocity of the stone
------------
The 2nd term has only to do with the downward
force of gravity
-------------
The stone will be at a height of m on its
way up and also again on its way down
-------------
Solve for

Divide both sides by

Complete the square:

Take the square root of both sides

And also, taking the positive square root
of the right side:

The rock is at a height of 50 m at .978 sec
and also at 10.222 sec
-------------
Here's the plot:

The points ( .978, 50 ) and ( 10.222, 50 )
look very possible. Hope this helps.

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