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 = 1.4 m1.6 m3.5 kg7.5 kg

A pendulum is made of a uniform slender rod (3.5 kg, 1.4 m long) pivoted at its top end O, with a solid sphere of mass 7.5 kg and radius 0.2 m fixed to its lower end. The centre of the sphere is 1.6 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3.5 kgL = 1.4 mmsphere = 7.5 kgr = 0.2 md = 1.6 m
IO = kg·m²
2.Easy
Or = 0.25 mL = 0.7 m0.95 m3.5 kg7 kg

A pendulum is made of a uniform slender rod (3.5 kg, 0.7 m long) pivoted at its top end O, with a thin solid disc of mass 7 kg and radius 0.25 m fixed to its lower end. The disc swings in its own plane and its centre is 0.95 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3.5 kgL = 0.7 mmdisc = 7 kgr = 0.25 md = 0.95 m
IO = kg·m²
3.Medium
4 kgaαM = 17.5 kgR = 0.1 m

A 4 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 17.5 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 acceleration a of the block.

m = 4 kgM = 17.5 kgR = 0.1 mg = 9.81 m/s²
a = m/s²
4.Medium
0 → 2200 rpmI = 36 kg·m²

A motor brings a flywheel with a moment of inertia of 36 kg·m² from rest up to 2200 rpm in 26 s. Ignoring losses, find the average power Pavg it delivers, in kW.

I = 36 kg·m²n = 2200 rpmt = 26 s
Pavg = kW
5.Hard
disc: 27 kgring: 1 kgn1​ = 100 rpm

A uniform solid disc (mass 27 kg, radius 0.2 m) spins freely at 100 rpm about a vertical frictionless shaft. A thin ring of mass 1 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 = 27 kgMring = 1 kgR = 0.2 mn1 = 100 rpm
ΔE = J
6.Hard
2 m/sω

A solid cylinder of mass 10.5 kg rolls without slipping at 2 m/s. What percentage p of its total kinetic energy is rotational?

m = 10.5 kgv = 2 m/sI = ½·m·r²
p = %

Answer key

  1. 1. IO = 21.61 kg·m²
  2. 2. IO = 7.108 kg·m²
  3. 3. a = 3.078 m/s²
  4. 4. Pavg = 36.75 kW
  5. 5. ΔE = 2.042 J
  6. 6. p = 33.33 %

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