# The velocity of a particle at the origin.

## Homework Statement

A particle moves according to the position function x(t)=ct2+bt where c=3m/s2 and b=-7m/s. Find the velocity at the origin.

2. The attempt at a solution
I tried just taking the derivative and setting t=0 to the equation as so:
vx(t)=6t-7=6(0)-7=-7 m/s
Although, when I put the answer into WebAssign it says I'm incorrect. I'm not looking for a definite answer since this is my homework but would just like to understand what I am doing wrong.

## The Attempt at a Solution

Related Introductory Physics Homework Help News on Phys.org
Maybe they're looking for the velocity at the other time the particle is at the origin?

I'm under the impression that the origin means they want me to solve it at t=0. What other origin could they be asking for?

I guess they mean the origin of the coordinate system, i.e. x=0. You usually say t=0 rather than the slightly ominous "the origin of time".

Yeah I just tried now to solve it at x=0 where I find that,
x(t)= 3t2-7t
0=3t2-7t+0constant
Then I treated it like a quadratic:
t=7+√[72-4(3)(9)] = 7/3s
2(3)
Then I put 7/3s into the formula...and...I got it right, thanks so much.