Block $$\(Y\)$$ with mass $$\(m_{Y}\)$$ falls onto and sticks to block $$\(X\)$$, which is attached to a vertical spring, as shown in Figure 1. A short time later, as shown in Figure 2, the blocks are momentarily at rest. At that moment, block $$\(Y\)$$ exerts a force of magnitude $$\(F_{\text {down }}\)$$ on block $$\(X\)$$, and block $$\(X\)$$ exerts a force of magnitude $$\(F_{\text {up }}\)$$ on block $$\(Y\)$$. Which of the following correctly relates $$\(F_{\text {up }}, F_{\text {down }}\)$$, and $$\(m_{Y} g\)$$ at the instant (A) $$\(\left(F_{\text {up }}=F_{\text {down }}\right)> m_{Y} g\)$$ (B) $$\(\left(F_{\text {up }}=m_{Y} g\right)> F_{\text {down }}\)$$ (C) $$\(m_{Y} g> F_{\text {up }}> F_{\text {down }}\)$$ (D) $$\(F_{\text {up }}=F_{\text {down }}=m_{Y} g\)$$ AP Physics 1: Algebra-Based Course and Exam Description Exam Information V. 1 | 174 Return to Table of Contents © 2021 College Board

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