Lesson: Conservation of Momentum

Two balls of equal masses collide with each other, as shown in the Before part of the diagram. Which of the four ways that the two balls could be moving as shown in the After part of the diagram does not conserve the balls’ total momentum?

During a game of pool, a cue ball that has a mass of 170 g moves along a pool table at a constant speed of 60 cm/s. The cue ball hits another ball, which has a mass of 160 g and is also moving along the table and in the same direction as the cue ball but at a constant speed of only 15 cm/s, as shown in the diagram. After the collision, the balls move together at the same constant speed. What is the speed of the balls after the collision? Round your answer to the nearest centimeter per second.

During a game of pool, a cue ball that has a mass of 170 g moves along a pool table at a constant speed of 51 cm/s. The cue ball hits another ball, which has a mass of 160 g and is not moving, as shown in the diagram. After the collision, the balls move together at the same constant speed. What is the speed, in centimeters per second, of the balls after the collision? Round your answer to one decimal place.