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 Post subject: PHY - HelpPosted: Wed, 7 Dec 2011 09:31:40 UTC
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Joined: Wed, 7 Dec 2011 09:19:57 UTC
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Car A is traveling on a highway at a constant speed (VA)o= 100km/h and is 120m from the entrance of an access ramp when car B enters the acceleration lane at that point at a speed (VB)o =25 km/hr. Car B accelerates uniformly and enters the main traffic lane after traveling 70 m in 5s. It then continues to accelerate at the same rate until it reaches a speed of 100km/hr, which it then maintains. Determine the final distance between the two cars.

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 Post subject: Re: PHY - HelpPosted: Wed, 7 Dec 2011 18:10:41 UTC

Joined: Wed, 3 Dec 2008 11:17:17 UTC
Posts: 6
Car A is travelling on a highway at a constant speed of 100km/h and is 120m from the entrance of an access ramp.

100 km/h = 27.8 m/s

Car B enters the acceleration lane at that point at a speed of 25 km/hr

25 km/h = 6.95 m/s.

Car B accelerates uniformly and enters the main traffic lane after travelling 70 m in 5s.

It then continues to accelerate at the same rate until it reaches a speed of 100km/hr. which it then maintains.

Determine the final distance between the two cars.

CAR B

Ave, speed on the ramp

70 m / 5 s = 14 m/s

Final speed on the ramp

( 6.95 m/s + final speed) / 2 = 14 m/s

final speed = 21.05 m/s

acceleration on the ramp

(21.05 m/s – 6.95 m/s) / 5s = 2.82 m/s/s

time taken to reach top speed

(27.8 m/s – 6.95 m/s) / 2.82 m/s/s = 7.4 s

average speed

(6.95 m/s + 27.8 m/s) / 2 = 17.38 m/s

distance travelled

17.38 m/s x 7.4 s = 128.6 m

CAR A

Distance travelled

27.8 m/s x 7.4 s = 205.7 m

distance of A from B

120 m + 128.6 m – 205.7 m = 42.9 m

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