Questions: If a projectile is launched vertically upward from the ground with an initial velocity of 50 ft per sec, then neglecting air resistance, its height s (in feet) above the ground t seconds after projection is given by s=-16 t^2+50 t. Which equation should be used to determine the time at which the height of the projectile reaches 20 ft ? Choose the correct answer below. A. 20=-16 t^2 B. s=-16(20)^2+50 C. 20=-16 t^2+50 t D. s=-16(20)^2+50(20)

Transcript text: If a projectile is launched vertically upward from the ground with an initial velocity of 50 ft per sec, then neglecting air resistance, its height s (in feet) above the ground t seconds after projection is given by $s=-16 t^{2}+50 \mathrm{t}$. Which equation should be used to determine the time at which the height of the projectile reaches 20 ft ? Choose the correct answer below. A. $20=-16 t^{2}$ B. $s=-16(20)^{2}+50$ C. $20=-16 \mathrm{t}^{2}+50 \mathrm{t}$ D. $s=-16(20)^{2}+50(20)$