You are to drive to an interview in another town, at a distance of 350 km on an expressway. The interview is at 11:15 A.M. You plan to drive at around 100 km/h, so you leave at 8:00 A.M. to allow some extra time. You drive at that speed for the first 100 km, but then construction work forces you to slow to 55 km/h for 40 km. What would be the least speed needed for the rest of the trip to arrive in time for the interview?
(I have two answers to this question but I am not sure which is right, if you do answer please include your method for solving as well)
2007-08-26 07:58:28 · 3 answers · asked by lapyramid 5 in Science & Mathematics ➔ Physics
Ok, you have travelled 140km so far leaving you with 210km to go. You have alrady spent 1.72 hours on the road, (first hour at 100km/hr and 40km for 55/km/hr). You therefore are left with 210km divided by 1.5 hours to go. You must travel at least 140km/hr.
Edit: These number are roughly rounded off considering you're deciding between two answers you already have.
2007-08-26 08:11:44 · answer #1 · answered by Chris H 2 · 1⤊ 0⤋
You probably got the answer correct.
You leave at 8:00 - you drive 100 km/h for 100 km. How long did that take??? One hour. You are 250 km away.
So it is not 9:00 - and you have to slow down to 55 km/h for 2/3 of an hour. How far have you travelled??? - 55x2/3 = 110/3 = 36.66 km. It is now 9:40. You are 213.33 km away.
How fast do you have to drive to make it there just in time?
You have 1 hour and 35 minutes left. You will travel 213.33 km. What's the speed???
213.33/1.5833 = 134.7 km/hr.
You can drive faster and have some time to spare - but the question asked for the minimum speed to make it on time - so this should be the answer.
2007-08-26 08:15:42 · answer #2 · answered by Anonymous · 0⤊ 0⤋
The two previous answer are correct, but I thought I should point out something interesting in the question. Assuming that the entire distance could be traveled on the expressway, and at constant speed, you still wouldn't have made it on time.
Driving 350 km at 100 km/h would take 3.5 hours. You've only given yourself 3.25 hours to get there. Even your best case would end up with you being 15 minutes late for your interview.
Not a very good way to make a first impression.
2007-08-26 08:39:16 · answer #3 · answered by skeptik 7 · 2⤊ 0⤋