Rate of Descent Math Problem Help?

Question

A Plane descends to sea level from 12,000 ft after being airborne for 1.5 hours. The entire flight time is 2 hr. and 10 min. Determine the average rate of descent of the plane.

I have a few problems like this and i don't know where to start...I am a visual learner so specific steps/ formulas to getting the answer will definitely help me with the other ones!

Thanks A Lot...by the way the answer should come out to be 300ft/min!

Answer 1

Time of descent = Entire flight time - Time until start of descent

<=> Time of descent = 2h10 - 1h30 (in case you didn't notice, 1,5 hours is 1hour and 30 mins)

<=> Time of descent = 130 min - 90 min

<=> Time of descent = 40 min



Rate of descent = 12000ft/40min

<=> Rate of descent = 300ft/min



Extremely easy...

Answer 2

If you plotted this on a graph (with height descended on the y-axis, and time on the x-axis), you'd get two points. 2 hr 10 min = 2 hr + 10/60 hr = 2 + 1/6 hr = 2 1/6 hr. So the two points are (1.5, 12000) and (2 1/6, 0). Finding the average rate of descent is the same as finding the gradient of this straight line (We have assumed it to be a straight line).



(y2 - y1) / (x2 - x1) = Gradient

Gradient = (0 - 12000) / (2 1/6 - 1.5)

= -12000 / (2 1/6 - 3/2)

= -12000 / (13/6 - 3/2)

= -12000 / (2/3)

= -12000 * 3 / 2 = -36000 / 2 = -18000 ft / hr.



-18000 ft in 1 hr... and 1 hr = 60 minutes. So -18000/60 = -300 ft per minute. Ignore the negative sign, as height cannot be negative.



There you go. I hope that helps!



me07.



P.S. Rate = How much of something is done / Unit Time (per second, per minute etc.)



So on average, the plane descends 300 feet in 1 minute.

Answer 3

To do the calculation, keep it in feet, seconds, pounds. But since you asked, 18ft per second is about 12.27 miles per hour. (Just 18ft / 5280, and then multiply that answer by 60 seconds and then 60 minutes.) This is a very simple problem because you have constant acceleration. Just ... Velocity = change in distance / change in time or compactly, v = x / t solve for t ... t = x / v and ... t = 800 ft / 18 ft per second t = 44.44 seconds So it will be 44.44 seconds until you land, and your descent rate is 18 feet per second, or 12.27 miles per hour.