Question

A remote-control airplane descends at a rate of four feet per second. After six seconds it is 116 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. y – 116 = - 4(x – 6) 108 feet y – 6 = - 4(x – 116) 438 feet y – 4 = 116(x – 6) 236 feet y – 116 = - 6(x – 4) 92 feet

Answer 1

After 3 seconds it's been descending for 3 seconds at a rate of 2 feet per second. So it's gone down 6 feet, and now it's at a height of 67. So it started off at 73. 

Its height after x seconds is 73 - 2x. (73 to start off with, minus 2 feet per second that's passed.) 

After 8 seconds it will be at a height of 73 - 2*8 = 73 - 16 = 57.