A person travels by car from one city to another with different constant speeds between pairs of cities. She drives for 30.0 min at 80.0 km/h, 12.0 min at 100 km/h, and 45.0 min at 40.0 km/h, and spends 15.0 min eating lunch and buying gas. (a) Determine the average speed for the trip. (b) Determine the distance between the initial and final cities along this route.
2006-09-16 06:24:47 · 4 answers · asked by noNAMEneeded!!! 1 in Education & Reference ➔ Homework Help
1/2 hr x 80 km/h = 40 km
1/5 hr x 100 km/h = 20 km
3/4 hr x 40 km/h = 30 km
Total distance = 40+20+30 = 90 km (Answer)
Total time = 30 min + 12 min + 45 min + 15 min = 1 hr 42 min
1 hr 42 min = (60 + 42)/60 = 102/60 = 51/30 hours
Avg speed = distance/time = 90/(51/30) = (90 x 30)/51 = 2700/51 = 52.9 km/hr (Answer)
2006-09-16 06:39:46 · answer #1 · answered by bpiguy 7 · 0⤊ 0⤋
Average speed was 62 km/hr
Distance between two cities, was 90 km
Here's how:
You first find the distance traveled in each increment:
30 minutes @ 80 kn/hr = 40 km
12 minutes @ 100 km/hr = 20 km
45 minutes @ 40 km/hr = 30 km
the total of those numbers is your distance regardless of any breaks.
The average speed is your total distance (90km) times 60 (because it's PER HOUR), then multiplied by the total driving minutes (don't include the break since there were no km gained during the break)
Hope it helps.
2006-09-16 06:33:38 · answer #2 · answered by Anonymous · 0⤊ 0⤋
A.
V=d/t
V=(80km-h/[30min/60min] + 100km-h/[12min/60min] + 40km-h/[45min/60min] + 0km-hr/[15min/60min])/4
V=(80km-h/0.5h + 100km-h/0.2h + 40km-h/0.75h + 0km-hr/0.25h)/4
V=(160km + 500km + 53.333km + 0km)/4
V=713.333km/4
V=178.3325km
Seeing as how it is hours you need to first change the minutes to hours by dividing by 60, because there are 60 minutes in one hour. This changes the 30 min to 0.5 hr and the 46 min to 0.75 hr, 12 min to 0.2 hr and 15 min to 0.25 hr. You set up the equation as distance over time and add the three times then divide by three to find the average. This helps you to find the average speed or velocity.
You should be able to figure out B by solving the equation of v=d/t for D, then multiplying the beginning and end increments and subtracting them.
2006-09-16 06:39:36 · answer #3 · answered by bluecrystalsmile 2 · 0⤊ 1⤋
u should do ur homework own not to be sovled by others it wont help u in study.
2006-09-16 06:29:51 · answer #4 · answered by mahesh 1 · 0⤊ 0⤋