i have 50 minutes, this is the problem: an engineer in a train sees a car stuck on the track at a railroad crossing in front of the train. when the engineer first sees the car , the locomotive is 280m from the crossing and its speed is 23 m/s . if the engineers reaction time is .33 s what should be the magnitude of the minimum deceleration to avoid an accident? answer in m/s^2 if u could do this, plz try.....and show how. thanks
Hehe. We've had guys ask for help before with their homework, but this is the first time in the middle of a test!
lollll.......man its not a test, its this hw thing i gotta turn in online and i have 40 minutes....lol plzzzzzzzz help!
Engineers always speed up if a car is on the tracks ahead to decrease damage to the train's expensive wheels and to clear the path quickly. This is a trick question.
Just like the first rule they taught us as freshmen engineers is the first engineers on the scene of an accident should kill all the survivors. keeps the lawsuits down you know. and whoever asked the question, i assume you subtract reaction time*velocity from 280 (this is now the distance left to stop) and then divide that by 11.5 (the average speed as you decelerate from 23 to 0). this gives the number of seconds to stop. then divide 23(your original speed) by that number to get the acceleration. i think that should work but don't hold me to that.
280 meters 23 meters / second 0.33 second reaction time x 23 m/s = 7.59 meters travelled before reacting That means 272.41 meters to be travelled before stopping. d = (vi + vf)/2 * t We know d =272.41; vi = 23 m/s; vf = 0 m/s. Therefore, the time involved equals 23.68 seconds. d = vi * t + 1/2 * a * t^2 We know d = 272.41; vi = 23 m/s. t = 23.68 seconds. A = (d - vi * t) * 2 / t^2 A = -0.97 m / s^2 I think
apparently shanna cares far more about your academic well being than I do (even including the equations, units, and the answer)
hmm, a little late but let's see here. reaction time is 0.33 s times 23m/s = 7.667 m travelled before decleration. 280 m - 7.667 m = 272.3333 meters before collision. Vf = sqrt(Vi^2 + 2*a*d) 0 = sqrt(23^2 + 2*a*272.3333) 0 = 529 + a*544.666667 a = -529/544.6667 a = -0.971 m/s^2 at least that's what i get...
I dont know any of the formulas, but here is my guess... 280/23 = 12.1739 seconds until it hits. Assuming the speed is 23 meters per second So minus the .33 seconds for reaction time = 11.8439 seconds to stop Magnitude of minimum deceleration umm....what Shanna said.... try this page too http://cstl-cst.semo.edu/venezian/PH120/physics_120_test2.htm
I would have been able to answer this if I had been at a computer when you first posted it. I'm a physics superstar.
hmm.. I took physics last year and made an A but that was last year too bad i think i threw away my note cards with all those equations on them
hey guyz i appreciate all the help alot! i got the answer w/ like 5 minutes left. I got the same thing as those people who got -.971 and thats y i kept on missing it. The answer is actually .971, i think its becuz of the fact that it asked for magnitude...thx alot
Man, I wish I was still in school. How much fun with all this new technology. I will admit that once I hired a math tutor for 5$ to do my take home calculus exam. Perfect score. That's the only time I really cheated. I was just too tired to think about an exam that night. No guilt to this day. I just wasn't in the mood to work on that exam.
phislammajamma.. hmm i had a calculus take home test assigned today.. lol too bad its only like 1 tenth of the total test and we take the rest in class.. take home tests are fun.. gotta love that two days to work on two problems.. at least i go into the test pretty sure i have at least a 10 going
I took Level III physics in high school and got an 80. Physics is phun. I took first year physics in university and got a 50. Physics is dumb.
I am ashamed to say that I couldn't remember how to work that problem despite having a minor in science (16 hrs in Chemistry and 8 hrs in Physics)! It's really true that if you don't use something on a regular basis, then you forget how to do it. My Bachelor's degree is in math, and I guarantee you that I would have a hard time doing calculus or differential equations right now. Speaking of classes, I'm taking this damn Intro to Accounting class as part of a prerequisite for my MBA and I was forced to take it by correspondence--meaning I have to teach it to myself. I've been lucky that there are several CPAs at work that have helped me with previous problems, but right now I am baffled by this FIFO and LIFO crap on inventory.
