A projectile is thrown upward so that its distance above the ground after t seconds is h = -16t2 + 672t. After how many seconds does it reach its maximum height?

Question

anonymous · Answer

A. 21s
B. 31.5s
C. 42s
D. 10s

yrelhan4 · Answer

You know how to find maxima using differentiation?

campbell_st · Answer

do you know how to factor the quadratic of find the line of symmetry

anonymous · Answer

No, im not sure how to do his problem at all. Ive never been good with word problems.

anonymous · Answer

If you show me how to find the answer to this practice problem, ill be bale to figure out the answer to the actual problem i need

campbell_st · Answer

well the line of symmetry for a parabola $$y = ax^2 + bx + c$$ 

is given by 

$$x = \frac{-b}{2a}$$

the maximum height occurs on the line of symmetry 

so in your question you have  to find 

$$t = \frac{-b}{2a} $$

where b = 672 and a = -16

this will give the time when the maximum height occurs