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 = 0.6 m0.75 m1 kg3.5 kg

A pendulum is made of a uniform slender rod (1 kg, 0.6 m long) pivoted at its top end O, with a thin solid disc of mass 3.5 kg and radius 0.15 m fixed to its lower end. The disc swings in its own plane and its centre is 0.75 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 1 kgL = 0.6 mmdisc = 3.5 kgr = 0.15 md = 0.75 m
IO = kg·m²
2.Easy
Or = 0.05 mL = 0.7 m0.75 m2.5 kg9 kg

A pendulum is made of a uniform slender rod (2.5 kg, 0.7 m long) pivoted at its top end O, with a solid sphere of mass 9 kg and radius 0.05 m fixed to its lower end. The centre of the sphere is 0.75 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 2.5 kgL = 0.7 mmsphere = 9 kgr = 0.05 md = 0.75 m
IO = kg·m²
3.Medium
2 kgaαM = 12.5 kgR = 0.1 m

A 2 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 12.5 kg and radius 0.1 m that turns on a frictionless horizontal axle. The block is released from rest. Use g = 9.81 m/s². Find the speed v of the block after it has fallen 1 m.

m = 2 kgM = 12.5 kgR = 0.1 mg = 9.81 m/s²h = 1 m
v = m/s
4.Medium
5.5 kgaαM = 5.5 kgR = 0.4 m

A 5.5 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 5.5 kg and radius 0.4 m that turns on a frictionless horizontal axle. The block is released from rest. Use g = 9.81 m/s². Find the angular acceleration α of the pulley.

m = 5.5 kgM = 5.5 kgR = 0.4 mg = 9.81 m/s²
α = rad/s²
5.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 =
6.Hard
θ = 40°vs = 10 m

A thin hoop starts from rest and rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 10 m along the slope.

θ = 40°s = 10 mI = m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 2.128 kg·m²
  2. 2. IO = 5.48 kg·m²
  3. 3. v = 2.181 m/s
  4. 4. α = 16.35 rad/s²
  5. 5. μs = 0.2397
  6. 6. v = 7.941 m/s

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