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 = 0.15 mL = 1.3 m1.45 m5 kg9.5 kg

A pendulum is made of a uniform slender rod (5 kg, 1.3 m long) pivoted at its top end O, with a thin solid disc of mass 9.5 kg and radius 0.15 m fixed to its lower end. The disc swings in its own plane and its centre is 1.45 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 5 kgL = 1.3 mmdisc = 9.5 kgr = 0.15 md = 1.45 m
IO = kg·m²
2.Easy
Or = 0.15 mL = 1.4 m1.55 m0.5 kg8 kg

A pendulum is made of a uniform slender rod (0.5 kg, 1.4 m long) pivoted at its top end O, with a thin solid disc of mass 8 kg and radius 0.15 m fixed to its lower end. The disc swings in its own plane and its centre is 1.55 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 1.4 mmdisc = 8 kgr = 0.15 md = 1.55 m
IO = kg·m²
3.Medium
ω = ?2.5 kgL = 2.4 mm = 9.5 kg

A uniform slender rod of mass 9.5 kg and length 2.4 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 2.5 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 = 9.5 kgL = 2.4 mmball = 2.5 kgg = 9.81 m/s²
ω = rad/s
4.Medium
ω = ?L = 1 mm = 8 kg

A uniform slender rod of mass 8 kg and length 1 m is pinned at one end and released from rest in a horizontal position. 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 = 8 kgL = 1 mg = 9.81 m/s²
ω = rad/s
5.Hard
θ = 40°vs = 7 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Its radius is 0.25 m. Find its angular velocity ω after it has rolled 7 m along the slope.

θ = 40°s = 7 mI = (2/5)·m·r²g = 9.81 m/s²r = 0.25 m
ω = rad/s
6.Hard
θ = 30°a

A hollow sphere rolls without slipping down a slope inclined at 30° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 30°I = (2/3)·m·r²g = 9.81 m/s²
a = m/s²

Answer key

  1. 1. IO = 22.9 kg·m²
  2. 2. IO = 19.64 kg·m²
  3. 3. ω = 3.234 rad/s
  4. 4. ω = 5.425 rad/s
  5. 5. ω = 31.76 rad/s
  6. 6. a = 2.943 m/s²

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