A projectile is thrown upward so that its distance above the ground after t seconds is given by the function h(t) = - 16t2 + 640t. After how many seconds does the projectile take to reach its maximum height?

Question

rajee_sam · Answer

for maximum height find the first derivative and equate it to zero and find the value of t

anonymous · Answer

so t=o and solve it first?

anonymous · Answer

or h(t)=0?

rajee_sam · Answer

You know "derivatives" f'(x)

rajee_sam · Answer

maximum height is at the maximum point

rajee_sam · Answer

this is an inverted cup since the leading coefficient is negative

rajee_sam · Answer

find the vertex

anonymous · Answer

okay. thanks i think i understand it now. :)

rajee_sam · Answer

you are welcome

rajee_sam · Answer

I think it is 20 secs.

anonymous · Answer

that's what i got

anonymous · Answer

isn't that just the x in the vertex though?

rajee_sam · Answer

yes

rajee_sam · Answer

you can do it in two different ways

anonymous · Answer

so next step is using the 20 and find y?

rajee_sam · Answer

instead of finding the vertex in a tedious process just take the first dervative and equate it to zero

anonymous · Answer

okay...

rajee_sam · Answer

The question is just about time it takes to reach the max. height

anonymous · Answer

oh so 20 seconds, that's all?

rajee_sam · Answer

yes

rajee_sam · Answer

They are just asking you the time

anonymous · Answer

okay, thank you very much for the help :D

rajee_sam · Answer

Hi the time will be 10 secs not 20