Physics — Free-Body Diagram Set (Four Cases)
Four worked free-body diagrams — block at rest, block on a rough incline, accelerating lift, skydiver at terminal velocity — each with forces resolved and the resulting acceleration stated.
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"label": "A · Block at rest on a horizontal table",
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"label": "Normal force N_A = 19.6 N, vertically up from the table",
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"label": "Equilibrium: the table pushes back with exactly the weight, so Fnet(A) = 0.00 N and a(A) = 0.00 m/s² — 'at rest' and 'no resultant force' are the same statement.",
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"label": "B · Block sliding down a rough 30° incline",
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"label": "Normal N_B = 33.97 N, perpendicular to the slope",
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"label": "Kinetic friction f_B = 6.794 N up the slope, μ(f_B) = 0.20",
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"label": "Block B · m(B) = 4.0 kg on a 30° incline, free to slide along it",
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"label": "Resolve along the slope: Fnet(B) = 12.82 N down the incline, so a(B) = 3.205 m/s². Perpendicular to it the forces balance, which is what fixes the normal force.",
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"label": "Weight W(B) = 39.23 N (m·g), vertically down — not along the slope",
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"label": "C · Passenger in a lift accelerating upward",
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"label": "Floor pushes up: N_C = 826.5 N",
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"label": "Newton's second law: N_C minus W(C) is the net force Fnet(C) = 140.0 N upward, m(C)·a(C) — the scales read 826.5 N while the lift accelerates and 686.5 N at constant speed.",
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"label": "Passenger C · m(C) = 70 kg · a(C) = 2.0 m/s² upward",
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"label": "Weight W(C) = 686.5 N (m·g), unchanged by the acceleration",
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"label": "D · Skydiver at terminal velocity",
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"label": "Drag D_D = 784.5 N, opposing the motion",
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"label": "Drag grows with v² until it equals the weight; then Fnet(D) = 0.0 N and the speed stops changing (about 43 m/s for ρ of 1.2 kg/m³ and C_dA of 0.70 m²).",
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"label": "Skydiver D · m(D) = 80 kg · falling at terminal velocity",
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