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You are jumping on a trampoline. For one jump, your height y (in feet) above the trampoline after t seconds can be represented by y= -16t^2+24t. How many seconds are you in the air?

Sagot :

Answer:

[tex]1.5\; \rm s[/tex].

Step-by-step explanation:

The person in this question is in the air whenever the height is greater than [tex]0[/tex].

The graph of [tex]y = -16\, t^{2} + 24\, t[/tex] is a parabola opening downwards. Rearrange and find values of [tex]t[/tex] that would set this expression to [tex]0[/tex].

[tex]\begin{aligned}y &= -16\, t^2 + 24\, t \\ &= t\, (-16\, t + 24) = -8\, t\, (2\, t - 3)\end{aligned}[/tex].

The first factor, [tex]t[/tex], suggests that [tex]t = 0[/tex] would set this expression to [tex]0[/tex]- quite expected, since the person is on the ground right before jumping.

The second factor, [tex](2\, t - 3)[/tex], suggests that [tex]2\, t = 3[/tex] (in other words, [tex]t = 3/2 = 1.5[/tex]) would also set this expression to [tex]0[/tex]. Hence, this person would be once again on the ground [tex]1.5[/tex] seconds after jumping.

Hence, this person is in the air between [tex]t = 0[/tex] and [tex]t= 1.5[/tex] for a total of [tex]1.5\; \rm s[/tex].