Lightweight Ninjas

Last week I gave a simple quiz to one of my classes on momentum.  Here is a problem quoted directly from the quiz:

2.    If a .55 kg ninja throwing star embeds itself in a stationary 3 kg block, what will be the speed of the block + star after the collision?  The star slams into the block at 5 m/s.

And here are the questions that followed:
"Don't we need to know the mass of the star?" ("It's given!" I respond)
"Why do you give us the mass of the ninja - we don't need that, do we?" ("That's a very small ninja!" I reply)
"This question is very poorly written." (*sigh*)

In the end, about half the class was confused by the question and the other half (including me) was mystified by their confusion until I realized the confused half never encounter the word 'ninja' as a adjective...

For the record, this is the first result when image googling 'ninja throwing star':


For fun, I googled ".55 kg ninja" and I did get this result:

Hmm... next year I will add a picture of the throwing star.  For the sticklers out there, I made the star very heavy so I could count points off when some students inevitably neglect the mass of the star when calculating the final momentum.  (experience & ease of grading trumps realism every time!)