Question

if a projectile is launched vertically upward from the ground with an initial velocity of 40 ft per sec, neglecting air resistance, its height s (in feet) above the ground t seconds after projection is given by s = - 16t² + 40t. which equation should be used to determine the time at which the height of the projectile reaches 30 ft? choose the correct answer below. a. s = - 16(30)² + 40(30) b. 30 = - 16t² + 40t c. s = - 16(30)² + 40 d. 30 = - 16t²

Explanation:

Step1: Identify the given height

We know the height formula is $s=-16t^{2}+40t$ and we want to find $t$ when $s = 30$.

Step2: Substitute the height value

Substitute $s = 30$ into the height - time formula, getting $30=-16t^{2}+40t$.

Answer:

B. $30=-16t^{2}+40t$