In the laboratory, two carts on a track collide in the arrangement shown in the preceding figure. Before the collision, the $$\(2-\mathrm{kg}\)$$ cart travels through pho- togate 1 , which measures its speed; the $$\(0.25-\mathrm{kg}\)$$ cart is initially at rest. After the collision, the carts bounce off one another. Photogate 2 measures the speed of each cart as it passes. A student is concerned about his experimental results. When he adds the momentum of both carts after collision, he gets a value greater than the momentum of the $$\(2-\mathrm{kg}\)$$ cart before collision. Which of the following is a reasonable explana- tion for the discrepancy?

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