applied maths Question 2.E 2

infinitymail · 30-09-2012 3:26pm #1

Hi all
I could do with some help for applied maths Question 2.E 2 in Fundamental applied maths 2nd edition.
"A car moves with acceleration 3a and deceleration 5a. Find in terms of k, the time taken to cover a distance 90 ak squared from rest to rest.
(i) subject to speed limit of 15 ak
(ii) subject to no speed limit"

for part (ii) is V set to k ?

Thanks

Iderown · 30-09-2012 9:09pm

Sketch the speed vs time graphs

infinitymail · 01-10-2012 10:46pm

The graph is not really a problem for me. Its just a upturned v shape.
I'm sure somebody has an answer.

FoxT · 02-10-2012 4:04pm

Subject to no speed limit is possibly simpler, so tackle that first I suggest.

At time t=0, car starts accelerating at 3a.
at time t=t1, car starts decelerating at 5a.

at time t1+t2, car is at rest.

1 - express the total time (t1+t2) in terms of t1, call this T.

2 - How far has the car travelled? Figure this out from t=0 to t1, and from t1 to t2, and add them. Then, express your answer in terms of T.

now you set that equal to 90ak^2

So you get 90ak^2 = some function f(a,T)

and use this to express T in terms of k.

applied maths Question 2.E 2

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