A car travels up a hill at a constant speed of 36 km/h and returns down the hill at a constant speed of 57 km/h. What is the average speed for the round trip.
2006-08-31 10:01:53 · 7 answers · asked by benzene boy 1 in Science & Mathematics ➔ Physics
Let the distance (one side) be D
time taken to travel at 36Km/h = D/36
time taken to travel at 57 Km/h = D/57
total time taken = D/36 + D/57
= Dx(36 + 57) / 36x57 = Dx 93 / 36x57
Total distance covered = D + D = 2D
So, avg speed = 2D/ (Dx 93 / 36x57) = 44.12 Km/h
2006-08-31 10:23:22 · answer #1 · answered by DG 3 · 6⤊ 1⤋
44.12903226 km/h
One assumes the distance is the same up and down - let it be 1 km (it doesn't matter). One also assumes that there is no turnaround time at the top, amongst other things! The situation becomes more realistic if you specify a road going over a mountain where the distance to the summit is the same on both sides - then the car doesn't stop at the top and you can talk about an average speed up and an average speed down. But that's splitting hairs!
The time taken up the hill is 1/36 = 0.027777778 hrs and the time taken down the hill is 1/57 = 0.01754386 hrs. Therefore the total time taken is 0.045321637 hrs for 2 km. The average speed is the total distance divided by the total time.
2/0.045321637 = 44.12903226 km/h
2006-08-31 10:12:34 · answer #2 · answered by Owlwings 7 · 5⤊ 0⤋
(36kph + 57Kph)
_______________
2 = 46,5 Avg KPH.
As the expression is based on average travel time = unit in motion, and the question clearly asks for avg speed , not distance factor, the expressions relating to turn around time and acceleration time, are not governing factors to the scientific notation in calculating avg kph expressed as trip speed.
Any calculation assuming one mile or 20 miles will not have any bearing on a constant speed calculation as the distance was not a factor in the base question. ie the 36 kph up and 57 kph down would be the same if the hill was 1 mile or 50 miles going up and the same coming down. You still maintain the same avg speed for the round trip of 46.5 kph
For example, if the hill were 3 miles up and 3 down for a combined total of 6 miles, the resulting speed would still be 36 kph going up and 57 kph going down for an avg speed of 46.5 kph .
Read the question.
Darryl S.
2006-08-31 10:11:05 · answer #3 · answered by Anonymous · 0⤊ 7⤋
Since it is the same distance on the way out and back:
(57 + 36) : 2 = 46,5 km/h
2006-08-31 10:07:07 · answer #4 · answered by Mike from BA 2 · 0⤊ 7⤋
Depends on how long it takes him to turn around and reach the speeds you mentioend! Given your unrealistic scenerio of going from 0-36km/hr and then 36-57 km/hr instanteously while also reversing directions instaneously then the first post is correct.
2006-08-31 10:07:26 · answer #5 · answered by murobertson 1 · 0⤊ 5⤋
(36+57)/2=46.5
2006-08-31 10:03:31 · answer #6 · answered by j_son_06 5 · 0⤊ 9⤋
Do your own homework.
2006-09-01 05:36:36 · answer #7 · answered by Anonymous · 0⤊ 8⤋