7
advanced-math

For a projectile h(t)=−16t2+64th(t) = -16t^2 + 64t, at what times is the height 48 ft?

A

1 second and 3 seconds

B

2 seconds

C

1 second and 2 seconds

D

3 seconds and 4 seconds

Correct Answer: A

Choice A is the correct answer. Set h(t)=48h(t) = 48.

  1. −16t2+64t=48-16t^2 + 64t = 48.
  2. Divide by -16: t2−4t=−3t^2 - 4t = -3.
  3. t2−4t+3=0t^2 - 4t + 3 = 0.
  4. Factor: (t−1)(t−3)=0(t - 1)(t - 3) = 0.
  5. Times: t=1t=1 and t=3t=3.

Choice B is incorrect because that is the max height time. Choice C is incorrect. Choice D is incorrect.

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Set 17: Quadratic Equations and Functions 17