# Thread: The equation of motion of a particle, where s is in meters and t is in seconds, is gi

1. ## The equation of motion of a particle, where s is in meters and t is in seconds, is gi

s=7t^3-3t

(a)Find the velocity and acceleration as functions of t.

v(t)=
a(t)=

(b) Find the acceleration after 7 seconds.

_______m/s^2

(c) Find the acceleration when the velocity is 0. (Round the answer to one decimal place) _______m/s^2

2. Originally Posted by plstevens
s=7t^3-3t

(a)Find the velocity and acceleration as functions of t.

v(t)=
a(t)=

(b) Find the acceleration after 7 seconds.

_______m/s^2

(c) Find the acceleration when the velocity is 0. (Round the answer to one decimal place) _______m/s^2
$v(t)=\frac{ds}{dt}(t)$

and:

$a(t)=\frac{dv}{dt}(t)=\frac{d^2 s}{dt^2}(t)$

RonL

3. so what do i do for b and c

4. Originally Posted by plstevens
so what do i do for b and c
b) You have your function for a(t) so what is a(7)?

c) When is v(t) = 0? Find that value of t and then find the acceleration at that time.

-Dan

5. i don't mean to be a dumby but i still don't get it

6. Originally Posted by plstevens
i don't mean to be a dumby but i still don't get it
If I gave you a function, for example, a(t) = 8t + 3 what would you tell me the value of a(7) is? Part b is exactly this, but of course with the function you derived in part a).

-Dan

7. I'm so sorry but thats not making sense

8. Originally Posted by plstevens
I'm so sorry but thats not making sense
In part a) your position function is given as $s(t) = 7t^3 - 3t$. From this you get that the acceleration function is
$a(t) = 42t$

What is the value of a(7), the value of the function a(t) when t = 7?

If you can't answer that, then I suggest you have a long talk with your instructor.

-Dan