Rigid-body rotation worksheet with answers

Free printable Rigid-body rotation worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
Or = 0.05 mL = 0.8 m0.85 m1.5 kg1.5 kg

A pendulum is made of a uniform slender rod (1.5 kg, 0.8 m long) pivoted at its top end O, with a solid sphere of mass 1.5 kg and radius 0.05 m fixed to its lower end. The centre of the sphere is 0.85 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 1.5 kgL = 0.8 mmsphere = 1.5 kgr = 0.05 md = 0.85 m
IO = kg·m²
2.Easy
L = 0.5 mGOd = 0.05 mm = 8.5 kg

A uniform slender rod of mass 8.5 kg and length 0.5 m rotates about an axis O perpendicular to the rod, 0.05 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 8.5 kgL = 0.5 md = 0.05 m
IO = kg·m²
3.Medium
n = 2300 rpmTb​ = 160 N·mI = 20.5 kg·m²

A flywheel with a moment of inertia of 20.5 kg·m² spins at 2300 rpm. A brake applies a constant friction torque of 160 N·m. How many revolutions N does the flywheel make before it stops?

I = 20.5 kg·m²n = 2300 rpmTb = 160 N·m
N = rev
4.Medium
L = 2.3 mm = 18.5 kgα

A uniform slender rod of mass 18.5 kg and length 2.3 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find the acceleration atip of the free end just after release.

m = 18.5 kgL = 2.3 mg = 9.81 m/s²
atip = m/s²
5.Hard
θ = 15°vs = 9 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 15° to the horizontal. Use g = 9.81 m/s². Its radius is 0.05 m. Find its angular velocity ω after it has rolled 9 m along the slope.

θ = 15°s = 9 mI = (2/5)·m·r²g = 9.81 m/s²r = 0.05 m
ω = rad/s
6.Hard
θ = 10°vs = 5 m

A hollow sphere starts from rest and rolls without slipping down a slope inclined at 10° to the horizontal. Use g = 9.81 m/s². Its radius is 0.35 m. Find its angular velocity ω after it has rolled 5 m along the slope.

θ = 10°s = 5 mI = (2/3)·m·r²g = 9.81 m/s²r = 0.35 m
ω = rad/s

Answer key

  1. 1. IO = 1.405 kg·m²
  2. 2. IO = 0.1983 kg·m²
  3. 3. N = 591.5 rev
  4. 4. atip = 14.71 m/s²
  5. 5. ω = 114.3 rad/s
  6. 6. ω = 9.134 rad/s

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