How can I get abs without hurting my back?

You are using your back to much. And you should be doijng crunches, nto situps. Situps are very bad for the back and do not work well for the abs. Crunches are the best. Its hard at first but when you are doing a crunch you chould be cintracting your stomach muscles to lift yourself off the ground, not your back. Start out wit a few sets of 5-10 a day. Once your stomach becomes stronger you will be able to utilize it more to do crunches, taking all of the stress off your back. Then you can increase. Also its not about how many crunches its about quality. When you do a crunch you should be stopiing at the peak holding for a second and then go back down. Once your abs get stronger I would really only recommend 3 sets of 15 with 3 different ab excersises. That doesnt sound liek much but it is alot. It adds up to 130 crunches. And if you do them the right way belive me it will burn. I alos recommend getting an ab ball. Its the best thing for abs and creates much less stress on the lower back.

you may want to use an exercise ball while doing your crunches, that way your back is well supported. also as a tip, don't try to pull on your neck while doing crunches, your arms should not do the work but your abs, hope this helps