Sphere A (mass m₁) is initially at rest; B (mass m₂) initially moves at speed v along +x. After collision B moves at speed v/2 along +y. The direction of A after collision makes what angle with the x-axis?
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Question

Sphere A (mass m₁) is initially at rest; B (mass m₂) initially moves at speed v along +x. After collision B moves at speed v/2 along +y. The direction of A after collision makes what angle with the x-axis?

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G1 Physics · Accepted Answer

Step 1 — Principle: Conserve the x- and y-components of momentum independently in an oblique collision. Step 2 — Working: From vector momentum: m₁Vₐ = m₂v î-(m₂v/2)ĵ. Step 3 — Working: Its x component is positive and y component negative, with |Vy/Vx|=1/2. Step 4 — Working: Therefore A moves in the fourth quadrant, angle tan⁻¹(1/2) below +x. Correct answer: C — tan⁻¹(1/2) below the +x-axis.