# Find the position function

• May 5th 2013, 11:56 AM
noork85
Find the position function

problem: A particle moves in a straight line and has acceleration 6cm/second square.Its initial speed is -2cm/second. Its initial position is given by f(0) = 9cm.
Find the position function f(x), where the input means the time.

here's what i know:
acceleration is f"(x) and speed is f'(x).

so i assume im looking for f(x).
but how do i setup the equation?

thanks!
• May 5th 2013, 01:24 PM
noork85
Re: Find the position function
• May 5th 2013, 04:12 PM
Prove It
Re: Find the position function
Quote:

Originally Posted by noork85

problem: A particle moves in a straight line and has acceleration 6cm/second square.Its initial speed is -2cm/second. Its initial position is given by f(0) = 9cm.
Find the position function f(x), where the input means the time.

here's what i know:
acceleration is f"(x) and speed is f'(x).

so i assume im looking for f(x).
but how do i setup the equation?

thanks!

Surely you know how to go from f''(x) to f(x) at least...
• May 5th 2013, 04:20 PM
noork85
Re: Find the position function
i do....this is what i came up with

f"(x)=6
f'(x)=6x+C...right?
• May 5th 2013, 04:39 PM
Prove It
Re: Find the position function
That's a good start. Now can you evaluate C?
• May 5th 2013, 05:01 PM
noork85
Re: Find the position function
C is a constant...how does it relate to speed?
• May 5th 2013, 05:12 PM
ManosG
Re: Find the position function
you have the initial value f'(0) = -2
• May 5th 2013, 05:41 PM
noork85
Re: Find the position function
f"(x)=6
f'(x)=6x+c
f'(x)=6x-2
f'(x)=3x^2-2x+D f(0)=9
f(x)=3x^2-2x+9
???
• May 5th 2013, 05:50 PM
Prove It
Re: Find the position function
Looks good. Of course, you can only assume that those constant values are the same as the values given because they are the initial values. If you had been given values at any other point in time, you would have had to substitute the points in and solve for the constant.