F(t) values graph, why doesn't this make sense?

[neutron star]

Homework Statement

http://img35.imageshack.us/img35/7035/picture18hl.png
http://img195.imageshack.us/img195/7315/picture19dq.png



http://img171.imageshack.us/img171/7427/picture20e.png
http://img16.imageshack.us/img16/8384/picture21v.png

Homework Equations

The Attempt at a Solution

I don't know why the values for c and e seem wrong to me. Shouldn't acceleration be positive at only t2 and t3? And velocity decreasing at t1, t4, and t5? Am I thinking of this the wrong way or too much like a physics problem?

 

[Mark44]

Acceleration is positive at t1 and t2, because the velocity is increasing at those points. Notice that at t3, the velocity is decreasing, which makes the acceleration negative at that point.

Velocity is decreasing at t3, t4, and t5. Not coincidentally, the acceleration is negative at these points.

 

[neutron star]

It said incorrect...

 

[Mark44]

It said incorrect...

It said incorrect for what?