Acceleration and Deceleration Experiment problem

[realslow]

Homework Statement

I did an experiment in which we gathered velocity-time data for a cart slowing down and speeding up on a ramp. The two acceleration values I calculated from the data were 0.4768m/s^2 and 0.4203m/s^2. Why are the values different (remember that there isn't any applied force in either direction)?

Homework Equations

The Attempt at a Solution

Well... I was thinking that the initial velocity, right after the cart was pushed upwards towards the sensor, is higher than the initial velocity (0 m/s) when the car stopped and moved back down (away from the sensor). But then again, I'm not sure as to whether it would affect the acceleration values.
I was debating whether or not friction had an effect, but I can't think of why the friction would be different for the deceleration and acceleration of the cart..
I think I'm having trouble understanding the forces acting on the cart...
I would very much appreciate some help, thank you!

 

[rl.bhat]

Hi realslow, welcome to PF.
I can't think of why the friction would be different for the deceleration and acceleration of the cart..
The frictional force is the same. But it acts in the opposite direction while going up and down. But the component of g is always in the downward direction.

 

[realslow]

Thank you very much!
I'm a happy student now hehe :)