A projectile is launched upward from ground level. Its height h (in feet) after t seconds is given by . At what time(s) will the projectile be at a height of 48 feet?
- At t = 1 second and t = 3 seconds (correct answer)
- At t = 1.5 seconds and t = 2.5 seconds
- At t = 2 seconds only
- At t = 0.75 seconds and t = 3.25 seconds
Explanation: Set h = 48: -16t² + 64t = 48. Rearranging: -16t² + 64t - 48 = 0. Divide by -16: t² - 4t + 3 = 0. Factoring: (t - 1)(t - 3) = 0, so t = 1 or t = 3 seconds. Choice B results from incorrectly setting up the equation as -16t² + 64t = 60. Choice C comes from finding only the vertex time (maximum height). Choice D results from computational errors in applying the quadratic formula.