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

• Feb 12th 2008, 12:03 PM
plstevens
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
• Feb 12th 2008, 01:11 PM
CaptainBlack
Quote:

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

$\displaystyle v(t)=\frac{ds}{dt}(t)$

and:

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

RonL
• Feb 12th 2008, 05:01 PM
plstevens
so what do i do for b and c
• Feb 12th 2008, 05:41 PM
topsquark
Quote:

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
• Feb 12th 2008, 05:50 PM
plstevens
i don't mean to be a dumby but i still don't get it
• Feb 12th 2008, 06:45 PM
topsquark
Quote:

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
• Feb 12th 2008, 06:47 PM
plstevens
I'm so sorry but thats not making sense
• Feb 12th 2008, 06:54 PM
topsquark
Quote:

Originally Posted by plstevens
I'm so sorry but thats not making sense

In part a) your position function is given as $\displaystyle s(t) = 7t^3 - 3t$. From this you get that the acceleration function is
$\displaystyle a(t) = 42t$

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