Step 1: Ok well the first way of doing it is, you take your image, and you drag it to the new layer button in the layer palette. Then you take the Single Column Marquee tool:

Then drag that line until you feel that that is where you want to start the blur. Then press Ctrl + T (transform tool) and just drag the middle little square to the way that the object is coming from. There you could leave it like that if you want, and that is also a nice little trick. But to make it look nice, I clicked on the Add layer mask item in the layers palette, and I clicked on the linear gradient , and I dragged a horizontal line to the object. Mess around with that and see what you get.

Step 2: The other way is you take your image, you duplicate it in the layers palette. Then you simply go to Filter -> Blur -> Motion Blur, chose an angle of 180 and 100 pixels.. then move the blurred copy so that the part where the object is supposed to not be blurry is right overtop the actual object (in the layer under). Then move the real object overtop of the blurred in the layers palette. Change your blur method from Normal to Multiply (or try a different one.. to get a unique effect). And you’re done!