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+--- Thread: Solve for elapsed time (/thread-10828.html)
Solve for elapsed time - DrD - 05-30-2018 09:13 PM
With these provided values, (including the units), how could the prime be made to find the elapsed time?
[CAS]
vi:=18.51_(m/s);
d:=79.8_(m);
a:=11.17_(m/s^2);
t=?
d=vi*t + 1/2 * a*t^2;
(Of course, the units could be removed, using left(var), and a mathematic result obtained; however it's the physical result that's desired).
-Dale-
RE: Solve for elapsed time - roadrunner - 05-30-2018 10:56 PM
Solve will do it if you use exact values. In CAS:
d:=(vi,t,a)->vi*t+(1/2)*a*t^2
then:
USIMPLIFY(solve((exact(d(18.51_(m/s),t,11.17_(m/s^2)))) = (exact(79.8_(m))),t))
gives:
{2.47014692829_(s),−5.78438148514_(s)}
-road
RE: Solve for elapsed time (Solved) - DrD - 05-31-2018 11:43 AM
Thanks, for the very helpful information, Road! Using exact(value) is the key to success, here. (Good catch on that ...!) In my case, even though [CAS] [Exact] checkbox was checked, I see, (now), that it says it only affects the "Returned" values.
(I wonder why it doesn't work, more generally?)
[CAS]
Code:
vi:=exact(18.51_(m/s));
d:=exact(79.8_(m));
a:=exact(11.17_(m/s^2));USIMPLIFY(solve(d = (vi*t+(1/2)*a*t^2),t));
t = {−5.78_(s), 2.47_(s)}
-Dale-