A few days ago
xolifes2sh0rtox

Help with functions – scenario represented by an equation?

I have about 10 of these for homework that I don’t understand. So could you help me with the first one, so I can use that problem as a reference? Thank you!!

If a rock falls from a height of 20 meters on Earth, the height H (in meters) after x seconds is approximately

H(x)= 20 – 4.9x^2

a. What is the height of the rock when x=1 second? x=1.1 seconds? x= 1.2 seconds?

b. When is the height of the rock 15 meters? When is it 10 meters? When is it 5 meters?

c. When does the rock strike the ground?

Top 2 Answers
A few days ago
bezi_cat

Favorite Answer

A.) This part of the problem gives you the x – values of three different periods of time. Simply substitute those values in for ‘x’ to get your answer.

H(1) = 20 – 4.9(1)^2

H(1) = 20 – 4.9(1)

H(1) = 20 – 4.9

H(1) = 15.1

H(1.1) = 20 – 4.9(1.1)^2

H(1.1) = 20 – 4.9(1.21)

H(1.1) = 20 – 5.929

H(1.1) = 14.071

H(1.2) = 20 – 4.9(1.2)^2

H(1.2) = 20 – 4.9(1.44)

H(1.2) = 20 – 7.056

H(1.2) = 12.944

B.) This part of the problem gives you the values for “H(x)” – which is essentially the y value instead of the value. Again, use substitution and then solve for the time (the x) instead.

15 = 20 – 4.9x^2

4.9x^2 = 5

x^2 = 1.02041

x = 1.01053

10 = 20 – 4.9x^2

4.9x^2 = 10

x^2 = 2.04082

x = 8/7

5 = 20 – 4.9x^2

4.9x^2 = 15

x^2 = 3.06122

x = 1.74964

C.) This part is similar to part ‘b,’ but you have to decide what height you want to substitute into the equation. Because you are being asked when the rock strikes the ground, you’re looking for the rock’s height on the ground. This, of course, would be zero.

0 = 20 – 4.9x^2

4.9x^2 = 20

x^2 = 4.08163

x = 2.02031

The rock strikes the ground after about 2.02031 seconds.

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A few days ago
Anonymous
for A) i think you just substitute x for a number then you do the equation on the right to get the height

ex- H=20-4.9(1)^2

ex.H=20-4.9(1.1)^2

also what doe ^ mean?

if i know what ^ is i could probley help you with the rest because i just did these ind of questions a few months a ago and i still remember how to do it

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