Question

A bungee jumper leaps off a cliff 122 meters from the ground. Her cord, when fully stretched, is 72 meters long, and it takes 6 seconds after the jump for it to extend fully. The distance between e jumper and the ground as a function of time can be modeled as a quadratic function. Which equation represents her distance from the ground as a function of time?

Answer 1

Answer:

Answer is B.

Step-by-step explanation:

You can solve this by recognizing the vertex and the y-intercept of the quadratic equation based on the information provided.

The vertex occurs 6 seconds into the jump, when the cord is fully stretched to 72m, before it starts to contract again. This is when the jumper is closest to the ground, 122-72 = 50m above the ground. Notice the jumper never reaches the ground because the cord is only 72m long - it can't make it the full 122m - so there will not be an x-intercept (or t-intercept in this case). Anyway - the vertex is (6,50) using this information.

The y-intercept is the point at which t=0, the beginning of the jump. At the beginning of the jump, the jump is still on top of the cliff, 122m up. So the coordinates of the y-intercept are (0,122).

Now plug these values into the vertex form of the quadratic formula and solve for a:

$f(t) = a(t-h)^2+k\\122=a(0-6)^2+50\\72 = 36a\\a=2$

This means our general equation (in vertex form) for this scenario is:

$f(t)=2(t-6)^2+50$

Our answer options are in standard form, so just expand the vertex form of the equation to finish:

$f(t)=2(t-6)^2+50\\f(t)=2(t^2-12t+36)+50\\f(t)=2t^2-24t+72+50\\f(t)=2t^2-24t+122$

Answer 2

Answer:

Step-by-step explanation:okay

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