The height of a small rock falling from the top of a 124-ft-tall building with an initial downward velocity of –30 ft/sec is modeled by the equation h(t) = –16t2 – 30t + 124, where t is the time in seconds. For which interval of time does the rock remain in the air?

The rock hits the ground when its height is 0. Solving −16t² − 30t + 124 = 0 gives t = 2 and t = −31/8; the negative time is not physically relevant. The rock is in the air after it is released at t = 0 and before it reaches the ground at t = 2, so the interval is 0 < t < 2, choice C.

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