Flying with no wind, a plane makes an 840 mile trip in 6 hours. On the return trip, the plane flies with a 70 mi/h wind. Write expressions for the total time, toal distance, and average speed.
I need to see how you arrived at the answer along with the answer. =)
2007-04-17 05:08:12 · 8 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
First we need to calculate the outgoing speed = distance /time= 840/6= 140 mph
The total return speed = outgoing speed + wind speed = 140+ 70 = 210mph.
Total distance = outgoing distance + return distance
As outgoing distance= return distance
Total distance = 2*outgoing distance = 2*840= 1680miles
Total time = outgoing time + return distance/return speed
Total time = 6 + 840/210 = 6 + 4 = 10hours.
Average speed = total distance / total time = 1680/10 = 168mph.
2007-04-17 05:17:18 · answer #1 · answered by The exclamation mark 6 · 0⤊ 0⤋
This is a d=rt problem, where d=distance, r=rateofspeed, and t=timetraveled.
Remember that average speed = total distance over total time.
Going there:
840 = rateofspeed * 6 so rateofspeedgoingthere=140
Coming back:
Here their speed is increased by wind so they are not traveling at 140mph but 140+70 or 210mph.
840 =(210)*Time so timetraveled = 4hours
Now we can find the total time for the journey by adding these 4 hours to the 6hours spent going there.
Total time = 6 +4 = 10
Total Distance on the other hand is just found by doubling the 840 miles going either way. The roundtrip distance is
d = 2(840) = 1680 miles.
Thus, the Average Speed is our total distance divided by the total time or 1680/10 = 168 mph.
Hope this helps! If they were flying against the wind, then you would subtract the wind speed from their initial velocity to get their true rate of speed.
2007-04-17 12:23:37 · answer #2 · answered by Number Power 3 · 0⤊ 0⤋
Distance/Time = Rate : 840/6 gives you plane speed of 140 MPH in still air.
Distance/Rate = Time : With a 70 MPH wind, the airplane can now fly 210 MPH (windspeed + planespeed if with a tailwind), and will arrive in 840/210 Hours, or 4 hours.
Total time is 6 + 4 or 10 hours.
Total distance is 840 x 2 or 1680
Average speed = 1680/10 or 168 MPH
2007-04-17 15:04:22 · answer #3 · answered by Don E Knows 6 · 0⤊ 0⤋
Flying with no wind his rate was 840/6 =140 mph
Flying with the wind his rate would be 140+70 =210 mph
The time with wind is 840/210 = 4 hours
So Total time = 6+4 = 10 hours
Total distance was 2*840 = 1680 miles
Average Speed was 1680/10 = 168 mph
2007-04-17 12:22:15 · answer #4 · answered by ironduke8159 7 · 0⤊ 0⤋
total distance is 840 • 2 = 1680
still air speed is 840/6 = 140 mph.
time for return trip is 840/(140+70) = 840/210 = 4 hrs.
total time is 6 hrs + 4 hrs = 10 hrs.
average speed is total distance / total time = 1680/10 = 168 mph.
2007-04-17 12:17:34 · answer #5 · answered by Philo 7 · 0⤊ 0⤋
Outward speed = 140 mph
Return speed = 210 mph
Total distance = 1680 miles
Return time = 840/210 hours = 4 hours
Total time = 10 hours
Average speed = 1680 / 10 mph = 168 mph
2007-04-17 13:11:59 · answer #6 · answered by Como 7 · 0⤊ 0⤋
total distance: d= 2 * 840
total time: t = 6 + 840/(840/6 -70)
t = 6 + 840/70
average speed s=d/t
s= (2*840)/(6+840/70)
This assume that there is no wind on the outgoing flight . the question is open to interpretation
2007-04-17 12:32:00 · answer #7 · answered by bignose68 4 · 0⤊ 0⤋
6 hours without wind
840=6v
v=140
840=(140+70)t
t=4 hours with wind
average speed=(140+70)/2
=105 mi/h
2007-04-17 12:20:18 · answer #8 · answered by iyiogrenci 6 · 0⤊ 0⤋