Solve for elapsed time

[DrD]

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-

[roadrunner]

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

[DrD]

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-