# velocity-time graph question

Discussion in 'Physics' started by redacejr, Apr 26, 2008.

1. ### redacejr Thread Starter Active Member

Apr 22, 2008
85
0
a car travels at a constant velocity of 20m/s for 200 sec and then accelerates uniformly to a velocity of 30m/s over a period of 20 sec. this velocity is maintained for 200sec before the car is brought to rest with a uniform deceleration in 30 sec.

total distance travelled is 10950m as i found out in the first part of the question

now i have to find the average speed over the whole journey.

pls help me cos im really stuck

2. ### Papabravo Expert

Feb 24, 2006
12,284
2,723
Would it be the total distance divided by the total time? Do ya think...maybe...perhaps? Could it be that straightforward? Were they trying to confuse you with all that detail? Sneaky problem writers!

3. ### Caveman Senior Member

Apr 15, 2008
471
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All of the detail is needed for the first part of the question. The second part is as easy as Papabravo says.

4. ### mrmount Active Member

Dec 5, 2007
59
7
Assuming that you have calculated the distance properly, I would just divide it by the total time. I don't see any catch here... Shouldn't it be straight forward ?

5. ### Caveman Senior Member

Apr 15, 2008
471
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Checked the distance, looks good.

6. ### Abiy Fantaye New Member

Apr 30, 2008
2
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divide the area under distance Vs time graph to any parts and then divide the sum of this parts by the number of parts.

Good luck!!!!

7. ### Abiy Fantaye New Member

Apr 30, 2008
2
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keep in mind that the graph must be distance-time graph

8. ### triggernum5 Senior Member

May 4, 2008
216
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To figure it out graphically from the V-T graph, you could consider the area in the triangle of the accelerated velocity.. That area is 10 units (does correlate to meters, but is confusing since its offset from 0m/s), divide that by total # of seconds, and add that to the the intilial 20m/s

9. ### redacejr Thread Starter Active Member

Apr 22, 2008
85
0
thanks dudes, i forgot to close the tread couple of weeks ago =S, i did it using papabravo's method... total distance/time and i got full marks thanks

10. ### triggernum5 Senior Member

May 4, 2008
216
1
Wow, thats wierd.. If I had you at a level where v-t graphs were understandable, if graph work was the exercise I wouldn't accept the grade 4 solution, but cool anyway..