The velocity of a particle at the origin.

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Homework Help Overview

The problem involves determining the velocity of a particle at the origin based on its position function x(t) = ct² + bt, with specific values for c and b. The original poster is seeking clarification on the correct interpretation of "the origin" in this context.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to find the velocity by taking the derivative of the position function and evaluating it at t=0. Some participants question whether the problem requires finding the velocity at other times when the particle is at the origin, while others clarify the meaning of "the origin" in relation to time and position.

Discussion Status

Participants are exploring different interpretations of the problem, with some suggesting alternative approaches to finding the time when the particle is at the origin. There is acknowledgment of multiple valid solutions based on the problem's wording.

Contextual Notes

There is a discussion about the potential ambiguity in the term "origin," specifically whether it refers to t=0 or x=0, and how this affects the interpretation of the problem. The original poster expresses uncertainty about the feedback received from the homework platform.

MelissaJL
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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.
 
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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.



Answer ends like so,
vx=6(7/3)-7= 7m/s
 
There is an easier way to solve it, just factor out one of the t's:
x=ct^2+bt = t(ct+b),
for which x=0 when t=0 or t=-b/c. Both solutions are of course valid (based on the problem text), even if the homework website doesn't think so...
 
x(t) = 0 when t=2.3333333333
 

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