Question

A plane at an altitude of 20000 feet starts to descend for landing after flying for six hours. The entire flight time was 6 hours 40 minutes. Determine the average rate of descent of the plane

Answer 1

Answer: 500 feet per minute

Explanation:

Landing time 40min with an altitude of 20000 remaining

40=20000 | both sides /40

1=500

Answer 2

Check the picture below.

so, let's see, the plane departs from (0, 0), the origin, goes up to 20000 feet, sticks around flying for 6 hours, 6hrs = 3600 minutes, (6*60).

so the plane's descent starts off at the point (3600, 20000) down to (3640, 0) as you see in the picture, keeping in mind that average rate of change = slope.

`\bf (\stackrel{x_1}{3600}~,~\stackrel{y_1}{20000})\qquad (\stackrel{x_2}{3640}~,~\stackrel{y_2}{0}) \\\\\\ slope = m\implies \cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{0-20000}{3640-3600}\implies \cfrac{-20000}{40} \\\\\\ \cfrac{-5000}{1}\cfrac{ft}{minute}\implies -5000(ft)/(min)`

the slope is negative, since it's a descent, the plane is coming down, not going up over the minutes axis.