Yes, Stapel got my meaning... Google will get you the answers, but it's not going to teach you HOW to get the answers. It's like when I was in high school, we were allowed calculators for homework etc, but come test time, you'd better know how to do it on your own.
Unit conversions are NOT such a difficult concept that students should have to rely on someone/something to tell them the answers. Furthermore, when they get further along into things such as physics (even elementary physics), keeping track of units and expressing things in equivalent terms is VERY important.
There are reasons for exercises such as these... reasons that are defeated by using Google, as you suggest.