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 = 0.5 m0.55 m3 kg7 kg

A pendulum is made of a uniform slender rod (3 kg, 0.5 m long) pivoted at its top end O, with a solid sphere of mass 7 kg and radius 0.05 m fixed to its lower end. The centre of the sphere is 0.55 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3 kgL = 0.5 mmsphere = 7 kgr = 0.05 md = 0.55 m
IO = kg·m²
2.Easy
R = 0.45 mn = 600 rpm100 kg

A flywheel is a uniform solid disc of mass 100 kg and radius 0.45 m. It spins at 600 rpm. Find its kinetic energy Ek in kJ.

M = 100 kgR = 0.45 mn = 600 rpm
Ek = kJ
3.Medium
L = 0.8 mm = 17.5 kgα

A uniform slender rod of mass 17.5 kg and length 0.8 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find its angular acceleration α just after release.

m = 17.5 kgL = 0.8 mg = 9.81 m/s²
α = rad/s²
4.Medium
ω = ?2 kgL = 2.4 mm = 6 kg

A uniform slender rod of mass 6 kg and length 2.4 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 2 kg is fixed to its free end. Ignore friction and use g = 9.81 m/s². Find the angular velocity ω of the rod as it swings through the vertical position.

m = 6 kgL = 2.4 mmball = 2 kgg = 9.81 m/s²
ω = rad/s
5.Hard
θ = 40°a

A solid cylinder rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 40°I = ½·m·r²g = 9.81 m/s²
a = m/s²
6.Hard
θ = 40°a

A solid sphere rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Find the smallest coefficient of static friction μs that prevents it from slipping.

θ = 40°I = (2/5)·m·r²g = 9.81 m/s²
μs =

Answer key

  1. 1. IO = 2.375 kg·m²
  2. 2. Ek = 19.99 kJ
  3. 3. α = 18.39 rad/s²
  4. 4. ω = 3.197 rad/s
  5. 5. a = 4.204 m/s²
  6. 6. μs = 0.2397

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