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h(t)=-4.9t^(2)+9.8 t+39.2
Kaia throws a stone vertically upward from a bridge. The height, in meters, of the stone above the water 
t seconds after the throw can be modeled by the quadratic function given. How many seconds after the throw does the stone hit the water?
Choose 1 answer:
(A) 1
(B) 2
(C) 4
(D) 8

h(t)=4.9t2+9.8t+39.2 h(t)=-4.9 t^{2}+9.8 t+39.2 \newlineKaia throws a stone vertically upward from a bridge. The height, in meters, of the stone above the water t t seconds after the throw can be modeled by the quadratic function given. How many seconds after the throw does the stone hit the water?\newlineChoose 11 answer:\newline(A) 11\newline(B) 22\newline(C) 44\newline(D) 88

Full solution

Q. h(t)=4.9t2+9.8t+39.2 h(t)=-4.9 t^{2}+9.8 t+39.2 \newlineKaia throws a stone vertically upward from a bridge. The height, in meters, of the stone above the water t t seconds after the throw can be modeled by the quadratic function given. How many seconds after the throw does the stone hit the water?\newlineChoose 11 answer:\newline(A) 11\newline(B) 22\newline(C) 44\newline(D) 88
  1. Find when stone hits water: To find when the stone hits the water, we need to find when h(t)=0h(t) = 0.
  2. Set equation to 00: Set the equation to 00 and solve for tt: 4.9t2+9.8t+39.2=0-4.9t^2 + 9.8t + 39.2 = 0.
  3. Divide and simplify: Divide the entire equation by 4.9-4.9 to simplify: t22t8=0t^2 - 2t - 8 = 0.
  4. Factor quadratic equation: Factor the quadratic equation: (t4)(t+2)=0(t - 4)(t + 2) = 0.
  5. Solve for tt: Set each factor equal to 00 and solve for tt: t4=0t - 4 = 0 or t+2=0t + 2 = 0.
  6. Ignore negative solution: Solving t4=0t - 4 = 0 gives t=4t = 4 seconds.
  7. Final result: Solving t+2=0t + 2 = 0 gives t=2t = -2 seconds, but time can't be negative, so we ignore this solution.
  8. Final result: Solving t+2=0t + 2 = 0 gives t=2t = -2 seconds, but time can't be negative, so we ignore this solution.The stone hits the water after 44 seconds.

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