Okay, here's the problem: A 24 g bullet is fired horizontally, embedding itself in a 10 kg block initally at rest on a horizontal ice surface. The block slides the ice, coming to rest in 2.0 s at a distance of 60 cm from its original position. Assuming that the frictional force stopping the block was constant, calculate the velocity of the bullet. Okay, I use the m1v1 + m2v2 = m1v1' + m2v2' formula to determine the v12'. However, my answer is half of what the answer in the back of the book is (My answer is 125 m/s while the book's is 250 m/s). Now, I think my problem might have something to do with the frictional force, but I dont really know where to begin to factor in the friction because the actual frictional force nor the frictional constant is given... please help.