Question

30 points
A remote-control airplane descends at a rate of two feet per second. After three seconds it is 67 feet above the ground. Write the equation in point-slope form that models the situation. Then find the height of the plane after eight seconds.

Answer 1

Since the rate of descent is a constant this is a linear equation and can be expressed as:

h=vt+b, where h=feet, v=slope or rate, b=y-intercept (y value when x=0 which is the initial height)

h=-2t+b, using the point (3,67) we can solve for b, or the initial height

67=-2(3)+b

67=-6+b

73=b  so the initial height was 73 ft and the height equation is then:

h(t)=67-2t so when t=8 you have:

h(8)=67-2(8)

h(8)=67-16

h(8)=51 ft