A ball is thrown from an initial height of 1 meter with an initial upward velocity of 25/ms.The ball's height h (in meters) after t seconds is given by the following. h=1+25t-5t^2 Find all values of t for which the ball's height is 6 meters.
Round your answer(s) to the nearest hundredth.

Question

A ball is thrown from an initial height of 1 meter with an initial upward velocity of 25/ms.The ball's height h (in meters) after t seconds is given by the following.  h=1+25t-5t^2    Find all values of t for which the ball's height is 6 meters.
Round your answer(s) to the nearest hundredth.

koikkara · Answer

@kamelish Can you draw the picture and write down the given data, like $h=?$ etc ...

anonymous · Answer

it wont let me @Koikkara

phi · Answer

$$  h=1+25t-52t^2  $$
ball's height is 6 .  That means h is 6.
$$ 6 = 1+25t-52t^2  $$
put that in standard form
$$ -52t^2 +25t -5=0 $$
It looks like we should use the quadratic formula to solve for t
do you know the quadratic formula?

anonymous · Answer

its 5t^2 i made a mistake @phi

phi · Answer

that's good, a much nicer number
$$ -5t^2 +25t+1=6 \ -5t^2 + 25t -5= 0 $$
divide both sides by -5 (to simplify the equation a little bit)
$$ t^2 -5t+1=0$$
but you still need to use the quadratic formula. Do you know it ?

anonymous · Answer

i know it a little bit @phi

phi · Answer

Do you have time to see this https://www.khanacademy.org/math/algebra2/polynomial-and-rational/quad_formula_tutorial/v/using-the-quadratic-formula It is pretty good.

anonymous · Answer

t=4.79 or t=0.20?  @phi

phi · Answer

if you have multiple choice,  you can test each answer in the original formula
$$ 1+25t-5t^2 = 6 $$
and see if you get 6 for the left-hand side

anonymous · Answer

thnaks =) @phi