Question

a model rocket is launched from a raised plat form at aspeed of 192 ft per second its height is given by
h(t)= -16t^2+192t+20 (t=secs after launch)
about how many seconds does the object reach its maximum height?
A) 20
B) 6
C) 3
D) 8

Answer 1

Well how do you find the maximum?

Answer 2

thats what im confused about

Answer 3

Take the derivative and set it equal to 0, then solve for t

Answer 4

i get 6

Answer 5

Don't guess. How did you end up with 6?

Answer 6

set all the t to 0 right?

Answer 7

Wait what class is this for? Calculus?

Answer 8

college alg

Answer 9

do you know how to take derivatives?

Answer 10

not really

Answer 11

Well, are you supposed to know how to take derivatives in that class?

Answer 12

prof never said anything about it

Answer 13

Okay, so since you guys don't do derivatives, I guess we can do this another way. Just find the vertex of that parabola.

Answer 14

http://hotmath.com/hotmath_help/topics/vertex-of-a-parabola.html

Answer 15

ugh i dont get it :/

Answer 16

Get that equation into the form:
y = a(x – h)^2 + k

Answer 17

idk how

Answer 18

-16t^2+192t+20
is in the form
at^2+bt+c
We need to get it in a form:
y=a(x-h)^2+k

Answer 19

First rewrite the equation as:
-(16t^2-192t-20) = -( (4t)^2 - 2*4*24t - 20 )

Answer 20

then complete the square to get it in the form we need it in

Answer 21

-20

Answer 22

after i solve it

Answer 23

No don't solve it. Get it into the form that i was talking about, and that will give you your (h; k). h will be your answer

Answer 24

i dont know what variable represents what number

Answer 25

Ok man,
-32t+192=0. Solve for t, that will be your answer