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Entering a Freeway

by Musicman
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Musicman
#1
Jun25-06, 03:24 PM
P: 21
Entering the Freeway. A car sits in an entrance ramp to a freeway, waiting for a break in the traffic. The driver sees a small gap between a van and an 18-wheel truck and accelerates with constant acceleration along the ramp and onto the freeway. The car starts from rest, moves in a straight line, and has a speed of 30 m/s (67 mi/h) when it reaches the end of the 115 m long ramp.

Ok for the acceleration I got 3.91 m/s/s and got that it takes 7.61 s for the car to travel the length of the ramp, but I dont understand part C:

(c) The traffic on the freeway is moving at a constant speed of 30 m/s. What distance does the traffic travel while the car is moving the length of the ramp?

i got 117.4 m but idk
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Hootenanny
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Jun25-06, 03:30 PM
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Quote Quote by Musicman
Ok for the acceleration I got 3.91 m/s/s and got that it takes 7.61 s for the car to travel the length of the ramp.
These are both correct, however I think you have induced a rounding error, the time should be 7.67s
Quote Quote by Musicman
(c) The traffic on the freeway is moving at a constant speed of 30 m/s. What distance does the traffic travel while the car is moving the length of the ramp?

i got 117.4 m but idk
I'm afraid this is not correct. Don't forget the traffic is travelling at a constant velocity.
Musicman
#3
Jun25-06, 03:32 PM
P: 21
what did u get then? cuz im totally lost like i knew what i was doing for the first 2 parts but not this part.

Hootenanny
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Jun25-06, 03:34 PM
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Entering a Freeway

Quote Quote by Musicman
what did u get then? cuz im totally lost like i knew what i was doing for the first 2 parts but not this part.
I'm not giving you the answer . Think about traveling at constant velocity. What is the equation for uniform velocity? How do you define velocity?
Musicman
#5
Jun25-06, 03:38 PM
P: 21
x=v of x times t
Hootenanny
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Jun25-06, 03:40 PM
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Quote Quote by Musicman
x=v of x times t
Thats right, distance is equal to the product of velocity and time. Use it
Musicman
#7
Jun25-06, 03:42 PM
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well i put 29.75 and it said its wrong and it was my last submission so oh well, apparently 7.61 times 3.91 doesnt work.
Hootenanny
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Jun25-06, 03:45 PM
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Quote Quote by Musicman
well i put 29.75 and it said its wrong and it was my last submission so oh well, apparently 7.61 times 3.91 doesnt work.
3.91 is the acceleration of the car travelling up the ramp not the velocity of the cars travelling on the freeway which would be 7.66 x 30 = 230m


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