Question

X S2.0.2

Answer 1

9514 1404 393

Answer:

• 320 m after 8 seconds
• 5.6 seconds, 10.4 seconds to height of 290 m

Step-by-step explanation:

To find the height at 8 seconds, evaluate the formula for t=8.

  S(t) = -5t^2 +80t

  S(8) = -5(8^2) +80(8) = -320 +640 = 320

The height of the rocket is 320 meters 8 seconds after takeoff.

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To find the time to 290 meters height, solve ...

  S(t) = 290

  290 = -5t^2 +80t

  -58 = t^2 -16t . . . . . . . divide by -5

  6 = t^2 -16t +64 . . . . . complete the square by adding 64

  ±√6 = t -8 . . . . . . . . . take the square root

  t = 8 ±√6 ≈ {5.551, 10.449}

The rocket is at 290 meters height after 5.6 seconds and again after 10.4 seconds.