Question

An object is dropped from a small plane flying at a height of $1000cm$ above the ground. As the object falls, $d$, its distance above the ground after $t$ seconds is given by the formula below
$d=16t^2+1000$
How far above the ground is the object, when it has fallen for $4$ seconds?

• A. $984cm$
• B. $936cm$
• C. $872cm$
• D. $744cm$

Answer 1

Answer: (D)

$744cm$

given that

$H=1000cm$ height above the ground

$d$ is the distance above the ground after $t$ seconds

formula for distance $d$ is given wrong in the question

The correct formula is

$d=1000-16t^2$

at $t=0$

$d=1000-0=1000cm$

at $t=4$

$d=1000-16\times 4^{2}cm$

$d=1000-16\times 16cm$

$d=1000-256=744cm$

when it has fallen for $4$ seconds , the object is $744cm$ above ground