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/sci/ - Science & Math

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1833317 No.1833317 [Reply] [Original]

Ok /sci/ I'm hitting a mental block here, and I need some help with this physics question.
>Car P travels due east along a straight highway at a constant speed of 30m/s. at 9am P passes exit 17. At precisely the same moment car Q passes exit 16, traveling due west at a constant 26m/s. Slightly later car P and car Q pass the same point. Knowing the exits are exactly 7km apart how many minutes past 9am do the cars pass each other?

So they are both moving at a constant speed, so I know acceleration = 0. I know The velocity of each (30m/s, 26m/s) and I know the distance (7km) how would I set up this problem? I'm not sure what equation to use. I have made two distances, d1 and d2 (d2=7km-d1) but I still can't figure out how to set up this problem. Help would be greatly appreciated.

>> No.1833327

Two ways to think about it:

write equations for both cars (y=mx+b) and solve for intersection

Pretend the highway is actually a train, and one car isn't moving. Then its just a simple matter of figuring how long the other car takes to get to the first.

>> No.1833334

>>1833327 I don't understand. Why would I use slope intercept form?

>> No.1833345

30x=-26x+7

divide x by 60 for minutes.

>> No.1833382

yeah, the way i'd do this is by setting up a kinematic equation for the distance traveled by a vehicle at a certain speed, but it will be 7km minus what the other vehicle travels during the same time, so... 30t = 7,000 - 26t is what i would do. solve for t, that gives seconds, divide by 60 for minutes.