Advanced Math practice question

Answer: 2

h(t) = 15 when −5t² + 20t = 15, i.e. t² − 4t + 3 = (t − 1)(t − 3) = 0: t = 1 and t = 3. Between those times the ball is above 15 m, so for 3 − 1 = 2 seconds.

Common wrong answers

If you answered 1

1 is when the ball first reaches 15 m, not how long it stays above.

If you answered 3

3 is when it comes back down to 15 m.

If you answered 4

4 is the total flight time (h = 0 at t = 4), not the time above 15 m.

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