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Rod AB sliding over wheel C

Short answer

The rod slides over the wheel, so the point at C has velocity along the rod. Using v_A sinθ = ω·AC gives ω = 1.1749 rad/s counter-clockwise. Then v_B = v_A + ω×r_B/A yields v_B = 569.6 mm/s at 59.1° above horizontal.

Rod AB moves over a small wheel at C while end A moves to the right with a constant velocity of 635 mm/s. At the instant shown, determine (a) the angular velocity of the rod, (b) the velocity of end B of the rod. [Figure: rod AB inclined, resting on small wheel C at height 178 mm; A on the ground; horizontal distance from A to the foot of C is 254 mm; 508 mm marked along the rod.]

Setting up. The rod slides over the wheel at CC, so the point of the rod that is at CC moves along the rod. Let AA be the origin and θ\theta the angle of the rod with the horizontal, assuming AB=508AB = 508 mm measured from AA along the rod.

tan⁡θ=178254  ⇒  θ=35.02∘,AC=2542+1782=310.2 mm\tan\theta = \frac{178}{254} \;\Rightarrow\; \theta = 35.02^\circ, \qquad AC = \sqrt{254^2 + 178^2} = 310.2\ \text{mm}
            B
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       C o  <- wheel, 178 mm high
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    A *--+----> vA = 635 mm/s
      254 mm

(a) Angular velocity of the rod

Velocity of the rod point at CC: v⃗C=v⃗A+ω⃗×r⃗C/A\vec v_C = \vec v_A + \vec\omega\times\vec r_{C/A}. It must be along the rod, so its component perpendicular to the rod is zero. The component of v⃗A\vec v_A perpendicular to the rod is vAsin⁡θv_A\sin\theta, and the rotation contributes ω (AC)\omega\,(AC) in the opposite sense:

vAsin⁡θ=ω (AC)v_A\sin\theta = \omega\,(AC) ω=vAsin⁡θAC=635×sin⁡35.02∘310.2=1.1749 rad/s (counter-clockwise)\omega = \frac{v_A\sin\theta}{AC} = \frac{635\times\sin 35.02^\circ}{310.2} = 1.1749\ \text{rad/s (counter-clockwise)}

(b) Velocity of end B

v⃗B=v⃗A+ωk^×r⃗B/A,r⃗B/A=508(cos⁡θ i^+sin⁡θ j^)\vec v_B = \vec v_A + \omega\hat k\times\vec r_{B/A}, \qquad \vec r_{B/A} = 508(\cos\theta\,\hat i + \sin\theta\,\hat j) v⃗B=635i^+1.1749 (508)(−sin⁡θ i^+cos⁡θ j^)=(292.5 i^+488.8 j^) mm/s\vec v_B = 635\hat i + 1.1749\,(508)(-\sin\theta\,\hat i + \cos\theta\,\hat j) = (292.5\,\hat i + 488.8\,\hat j)\ \text{mm/s} vB=569.6 mm/sv_B = 569.6\ \text{mm/s}

at 59.1° above the horizontal, to the right.

Answer: ω=1.1749\omega = 1.1749 rad/s counter-clockwise; vB=569.6v_B = 569.6 mm/s at 59.1° above the horizontal. If the 508 mm is measured from CC instead of from AA, replace rB/Ar_{B/A} by AC+508=818.2AC + 508 = 818.2 mm.

✓ Answer checked by Claude Opus 5.5 (high effort)

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