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 = 0.2 mL = 0.5 m0.7 m3.5 kg8 kg

A pendulum is made of a uniform slender rod (3.5 kg, 0.5 m long) pivoted at its top end O, with a solid sphere of mass 8 kg and radius 0.2 m fixed to its lower end. The centre of the sphere is 0.7 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3.5 kgL = 0.5 mmsphere = 8 kgr = 0.2 md = 0.7 m
IO = kg·m²
2.Easy
Or = 0.15 mL = 0.6 m0.75 m2 kg6 kg

A pendulum is made of a uniform slender rod (2 kg, 0.6 m long) pivoted at its top end O, with a solid sphere of mass 6 kg and radius 0.15 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 kgL = 0.6 mmsphere = 6 kgr = 0.15 md = 0.75 m
IO = kg·m²
3.Medium
3 kgaαM = 12.5 kgR = 0.25 m

A 3 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 12.5 kg and radius 0.25 m that turns on a frictionless horizontal axle. The block is released from rest. Use g = 9.81 m/s². Find the acceleration a of the block.

m = 3 kgM = 12.5 kgR = 0.25 mg = 9.81 m/s²
a = m/s²
4.Medium
ω = ?L = 2.1 mm = 3.5 kg

A uniform slender rod of mass 3.5 kg and length 2.1 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 = 3.5 kgL = 2.1 mg = 9.81 m/s²
ω = rad/s
5.Hard
disc: 13 kgring: 9 kgn1​ = 1050 rpm

A uniform solid disc (mass 13 kg, radius 0.3 m) spins freely at 1050 rpm about a vertical frictionless shaft. A thin ring of mass 9 kg and the same radius is dropped onto it from rest, centred on the shaft, and the two quickly spin together. How much kinetic energy ΔE is lost in the process?

Mdisc = 13 kgMring = 9 kgR = 0.3 mn1 = 1050 rpm
ΔE = J
6.Hard
θ = 20°a

A solid cylinder rolls without slipping down a slope inclined at 20° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 20°I = ½·m·r²g = 9.81 m/s²
a = m/s²

Answer key

  1. 1. IO = 4.34 kg·m²
  2. 2. IO = 3.669 kg·m²
  3. 3. a = 3.182 m/s²
  4. 4. ω = 3.744 rad/s
  5. 5. ΔE = 2053 J
  6. 6. a = 2.237 m/s²

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