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ENGR5004 / Week 6
Dynamics L12 Worked example 3TutorialOld spec ENGR2162:115 min

ENGR216 Dynamics L12 worked example 3 (slides 17-20) official answers

In a four-bar linkage, link CD (0.6 m) is vertical with D pinned to the ground and C above it; link BC (0.6 m) is horizontal with B to the left of C and E its midpoint; link AB runs from the ground pin A (level with D) up to B at 30∘30^\circ to the horizontal. CD rotates anticlockwise at ωCD=6\omega_{CD} = 6 rad/s.

Find the velocity of point E (magnitude and direction) and the angular velocity of link AB.

Four-bar linkage: AB at 30 degrees from ground pin A up to B; BC horizontal, 0.6 m, with midpoint E; CD vertical, 0.6 m, down to ground pin D; omega_CD = 6 rad/s anticlockwise.
Four-bar linkage: AB at 30 degrees from ground pin A up to B; BC horizontal, 0.6 m, with midpoint E; CD vertical, 0.6 m, down to ground pin D; omega_CD = 6 rad/s anticlockwise.
Formulas you may need
  • Instantaneous centre of zero velocity: intersection of the normals to vB\mathbf v_B and vC\mathbf v_C; v=ω r/ICv = \omega\,r_{/IC} (learn this)
  • Fixed-axis rotation: v=ωrv = \omega r, perpendicular to the link (learn this)