A stone is thrown vertically upward at a velocity of 10 feet per second from a bridge that is 60 feet above the level of the water. The height h (in feet) of the stone at time t (in seconds) after it is thrown is given by h = -16t2 + 10 + 60.

(a) Find the time when the stone is again 60 feet above the water. sec

(b) Find the time when the stone strikes the water. (Round your answer to two decimal places.) sec

(c) Does the stone reach a height of 90 feet? O Yes O No​

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  (a) 0.625 seconds (rounds to 0.63)

  (b) 2.27 seconds

  (c) No

Step-by-step explanation:

(a) We want to find t such that h = 60

  60 = -16t^2 +10t +60

  0 = t(-16t +10) . . . . . . . . . subtract 60, factor

  t = 0  or  t = 10/16 = 5/8 = 0.625

The stone is again 60 feet above the water after 0.625 seconds.

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(b) We want to find t such that h = 0

  0 = -16t^2 +10t +60

  16t^2 -10t = 60

  16(t^2 -5/8t +25/256) = 60 +25/16 . . . . complete the square

  (t -5/16)^2 = 61.5625/16 = 3.84765625 . . . . simplify a bit

  t = 5/16 +√3.84765625 ≈ 2.274 . . . . square root, add 5/16

The stone strikes the water at about 2.27 seconds.

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(c) The equation above tells us the peak height of the stone is about 61.56 feet. It does not reach a height of 90 feet.

answer is the third choice:

3x^5+4x^4+x^3+2x^2-10x-7=0

step-by-step explanation: