[Phys-l] projectile motion lab

[FIZIX29@aol.com]

My high school students will be performing a projectile motion lab where they 
roll a marble down an inclined plane and off of the lab table.  Prior to the 
marble rolling off of the table in will pass between two photogates which will 
measure the time elapsed between them.  The students will measure the 
distance between the photogates, the time elapsed, and the height of the lab table.  
> From this they will predict where the marble will land.  Pretty standard stuff.

They will measure the time between photogates multiple (>10) times and 
compute the mean and standard deviation.  My question is how to grade the lab.  If 
the marble hits the line representing the predicted distance they will get some 
extra points.  If the line is not hit then I was thinking of grades based on 
fractions of the standard deviation but I don't have a good sense of 
reasonable values.

Any advice?

Thanks

Justin