tiger2k Posted January 21, 2004 Share Posted January 21, 2004 ok i know these are simple physics problems but im having problems with them, so don't bash at me for being stupid :unsure: An automobile traveling v = 95 km/h overtakes a L = 1.20 km long train traveling in the same direction on a track parallel to the road. If the train's speed is 80 km/h, how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2-34. [.25] _________ min [.25] _________ km What are the results if the car and train are traveling in opposite directions? [.25] _________ s [.25] _________ km and the other question im having problems with: A rocket rises vertically, from rest, with an acceleration of 3.2 m/s2 until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward. (Assume that the positive direction is upward.) in total theres 6 sub-questions that follow this one, i already answer the 1st 2 but can't get the others :( (a) What is the velocity of the rocket when it runs out of fuel? [.167] sqrt(7680) m/s (b) How long does it take to reach this point? [.167] 27.386 s © What maximum altitude does the rocket reach? [.167] ______ m (d) How much time (total) does it take to reach maximum altitude? [.167] ______ s (e) With what velocity does it strike the earth? [.166] ______ m/s (f) How long (total) is it in the air? [.166] ______ s if you know how to do them please help me out with an explanation on how you did it Link to comment Share on other sites More sharing options...
markwolfe Veteran Posted January 21, 2004 Veteran Share Posted January 21, 2004 An automobile traveling v = 95 km/h overtakes a L = 1.20 km long train traveling in the same direction on a track parallel to the road. If the train's speed is 80 km/h, how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2-34. The difference in speed is 15 kph. To solve, figure out how long it takes a car going 15kph to travel 1.2km. Then for total car travel time, use the overtake time times the car's real speed to find total distance. That should be enough help. I don't give out answers.. ;) Link to comment Share on other sites More sharing options...
tiger2k Posted January 21, 2004 Author Share Posted January 21, 2004 fair enought, lets see if i can figure out that one, thanks :) Link to comment Share on other sites More sharing options...
tiger2k Posted January 21, 2004 Author Share Posted January 21, 2004 ok, using that hint you gave me i got 7.6Km in 12.5Mins i hope thats right :yes: i'll see if i can figure out the backwards part but anyone has any idea about the secound problem? Link to comment Share on other sites More sharing options...
wilsons1179 Posted January 21, 2004 Share Posted January 21, 2004 A rocket rises vertically, from rest, with an acceleration of 3.2 m/s2 until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward. (Assume that the positive direction is upward.)in total theres 6 sub-questions that follow this one, i already answer the 1st 2 but can't get the others :( (a) What is the velocity of the rocket when it runs out of fuel? [.167] sqrt(7680) m/s (b) How long does it take to reach this point? [.167] 27.386 s ? What maximum altitude does the rocket reach? [.167] ______ m (d) How much time (total) does it take to reach maximum altitude? [.167] ______ s (e) With what velocity does it strike the earth? [.166] ______ m/s (f) How long (total) is it in the air? [.166] ______ s if you know how to do them please help me out with an explanation on how you did it ok for the rocket one © You will want to find part (d) first then do this part but to do this part you will want to use the equation y(t) = ?*(ay)*t^2 + voy*t + yo where ay will be -g and voy will be your veloctiy when it runs out of fuel and yo will be 1200 m (d) To figure out the time you will want to use that the (change in velcity)=a*t The change in velocity will be negative since it is slowing down so your time will be positive (which is always good:D:D (e) The easiest way to figure this out is to use the maximum height you get from part © then you will take that number and use it in this equation vy(t)2 = voy2 - 2g(y-yo) where vy(t) is what you are looking for voy would be zero for this part g-gravity and (y-yo) would be the answer from part © since yo would be the number from part © and y is zero for the ground you will have two negaitives to make the velocity you hit the ground with as positive Will post part (f) in a second cant see questio:):) Link to comment Share on other sites More sharing options...
wilsons1179 Posted January 21, 2004 Share Posted January 21, 2004 for part (f) you will want to use this equation vy = gt + voy where vy will be the velocity the rocket hits the ground with and then g- gravity and voy will be zero since at the begining of the freefall part it was at rest Then add this number to the solution to part (d) and you get the total time it was in the air Link to comment Share on other sites More sharing options...
wilsons1179 Posted January 21, 2004 Share Posted January 21, 2004 if you need more help let me know you can contact me by instant message if you need to Link to comment Share on other sites More sharing options...
tiger2k Posted January 21, 2004 Author Share Posted January 21, 2004 ok, thanks, let me try them out with the info you gave me, if i run into trouble i'll contact you :yes: Link to comment Share on other sites More sharing options...
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