Since the 2-watt jobber has to dissipate twice as much power as the smaller unit I would expect it to have double the surface area. So if they are the usual cylindrical striped resistors then the larger one could have either double the length or else 1.4 times the radius of the smaller one.
Ep= mgh
Ep = 40 x 9.8 x 10
Ep = 3920J
Ep = 3900J (2sf)
If no wire is going around the nail I'd say North