Question

An object moves so that at time t its position s is found using `s(t) = 5*cos(t)`. For what values of 't' does the object change direction?

Answer 1

It changes direction at `pi/2`, `(3pi)/(2)`, and onwards at `pi` intervals

Explanation:

`s(t)=5cos(t)`

The graph is of the form above, the amplitude is 5.

You can see that `y`, which in this case is `s`, first becomes -ve at `(pi)/(2)`. Half a cycle i.e `pi` radians later it becomes +ve again at `(3pi)/(2)`

So at every `pi` interval it changes direction.