Average Velocity: Find the Answer

[Qube]

Homework Statement

The coordinate of an object is given as a function of time by x = 7t - 3t^2, where x is in meters and t is in seconds. Its average velocity over the interval from t = 0 to t = 2 s is?

(1) -5 m/s (2) 5 m/s (3) 11 m/s (4) -11 m/s (5) -14.5 m/s

Homework Equations

Average velocity = change in position / change in time.

The Attempt at a Solution

Change in time = 2 seconds.

Change in position:

x(0) = 0.

x(2) = 14 - 12 = 2.

Change in position is 2.

Therefore avg. velocity is 2/2 or 1m/s.

Am I doing something wrong?

 

[TSny]

Your work looks correct to me. 1 m/s is the right answer.

[Edit: If the position function were x = 7t-3t³, then you would get one of the answers.]

 

[Qube]

That's odd, since I copied and pasted this problem from an old physics exam of my prof's. I guess I'll have to see him about there being no correct answer among the choices.