If an object is thrown vertically upward from a height of h 0 ft with an...

If an object is thrown vertically upward from a height of h ₀ ft with an initial speed of v ₀ ft/sec, then its height h (in feet) after t seconds is given by Make use of this formula in working Exercises 70–72.

A ball is thrown vertically upward from ground level with an initial speed of 64 ft/sec.

(a) At what time will the height of the ball be 15 ft? (Two answers.)

(b) For how long an interval of time will the height exceed 63 ft?