## anonymous one year ago The position of an object at time t is given by s(t) = -9 - 5t. Find the instantaneous velocity at t = 4 by finding the derivative.

1. IrishBoy123

${ds(t) \over dt} = v(t) = { d\over dt}(-9 - 5t)$ ${d \over dt} (-9) = ??$ ${d \over dt} (-5t) = ??$

2. anonymous

what? sorry that is confusing me

3. IrishBoy123

ok you are asked to find the derivative of: $$s(t) = -9 - 5t$$ that will give you an equation for the velocity $$v(t)$$ of the object. how do you propose to do that?

4. anonymous

v (t) = ds/dt?

5. wmj259

That is correct. The velocity is the derivative of the position function.

6. wmj259

If you plug in a specific time into the velocity function you find the INSTANTANEOUS SPEED.

7. anonymous

So if i put v (9) = ds/d(9)

8. anonymous

i mean 4

9. IrishBoy123

i strongly suggest you do the derivative first. then you will see :p

10. anonymous

Yeah see the problem is I dont know how to do any of this, like for this lesson i missed it in school, and im doing a review right now for the quiz tomorrow and i dont understand this at all

11. wmj259

@IrishBoy123, Yes that would make your night much easier. By taking the derivative of the position function you get the velocity function. But in this case its not much of a velocity FUNCTION then it is a velocity CONSTANT.

12. anonymous

sO IT WOULD BE a velocity constant? whats that

13. anonymous

@Loser66 @satellite73

14. wmj259

Yes, But if you take the derivative of the position function, what do you get?

15. anonymous

idk? how would i find that