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

 

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!

 

All of the detail is needed for the first part of the question. The second part is as easy as Papabravo says.

 

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 ?

 

Checked the distance, looks good.

 

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!!!!

 

keep in mind that the graph must be distance-time graph

 

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

 

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

 

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..