Bunuel
A model rocket is shot straight up in the air from ground level. After 2 seconds and then again after 3 seconds, its height is 96 feet. Which of the following equations could define rocket’s height, (h), as a function of the number of seconds after launch (t)?
(A) h = 10t^2 – 74t
(B) h = 8t^2 – 64t
(C) h = 64t – 8t^2
(D) h = 80t – 16t^2
(E) h = 96t – 10t^2
It takes 2 secs to reach height of 96 and then the rocket reaches the maximum height and falls back and at 3 secs, it is again at 96 feet. In another 2 secs i.e. total 5 secs after starting, it will touch the ground again.
The options give us the relation between t and h. We already know that when t = 2, h = 96, when t = 3, h = 96 and when t = 5, h = 0.
Put t = 2 in the options.
Option (A) first term is smaller than 74 - Eliminate
Option (B) first term is smaller than 64 - Eliminate
Option (C) if t = 2, 8t(8 - 2) = 96. Put t = 3, 8t(8 - 3) = 120 - Eliminate
Option (D) if t = 2, 16t(5 - 2) = 96. Put t = 3, 16t(5 - 3) = 96. Answer
Option (E) 96t is much greater than 40 - Eliminate
Answer (D)