Okay, I did this problem, and my answer disagrees with the book. A 15.0 g rubber bullet hits a wall with a speed of 150 m/s. It bounces straight back with a speed of 120 m/s. what is the change in momentum? I get: delta p=(m*v-i) - (m*v-f) delta p= (15.0g * 150 m/s) - (15.0 g - 120 m/s) = 15.0 g(150m/s - 120 m/s) = 15.0g * 30 m/s delta p = 450g * m/s = .45 kg * m/s the book says the answer is 4.05 kg * m/s Am I wrong?