Question

$h=-4.9t^2+25t$
The equation above expresses the approximate height $h$, in meters, of a ball $t$ seconds after it is launched vertically upward from the ground with an initial velocity of $25$ meters per second. After approximately how many seconds will the ball hit the ground?

• A. $3.5$
• B. $4.0$
• C. $4.5$
• D. $5.0$

Answer 1

Answer: (D)

$5.0$

When the ball hits the ground, $h=0$
$\Rightarrow -4.9t^2+25t=0$
$\Rightarrow 4.9t^2=25t$
$\Rightarrow t=0$ or $4.9t=25=>t$ is approximately equal to $5$
Thus, after $5$ seconds, the ball hits the ground.