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 = 0.6 m0.65 m5 kg6 kg

A pendulum is made of a uniform slender rod (5 kg, 0.6 m long) pivoted at its top end O, with a solid sphere of mass 6 kg and radius 0.05 m fixed to its lower end. The centre of the sphere is 0.65 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 5 kgL = 0.6 mmsphere = 6 kgr = 0.05 md = 0.65 m
IO = kg·m²
2.Easy
Or = 0.25 mL = 1.5 m1.75 m3.5 kg5 kg

A pendulum is made of a uniform slender rod (3.5 kg, 1.5 m long) pivoted at its top end O, with a thin solid disc of mass 5 kg and radius 0.25 m fixed to its lower end. The disc swings in its own plane and its centre is 1.75 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3.5 kgL = 1.5 mmdisc = 5 kgr = 0.25 md = 1.75 m
IO = kg·m²
3.Medium
0 → 1100 rpmI = 9.5 kg·m²

A motor brings a flywheel with a moment of inertia of 9.5 kg·m² from rest up to 1100 rpm in 23 s. Ignoring losses, find the average power Pavg it delivers, in kW.

I = 9.5 kg·m²n = 1100 rpmt = 23 s
Pavg = kW
4.Medium
13 kgaαM = 8 kgR = 0.15 m

A 13 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 8 kg and radius 0.15 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 1.5 m.

m = 13 kgM = 8 kgR = 0.15 mg = 9.81 m/s²h = 1.5 m
v = m/s
5.Hard
8.5 m/sω

A solid sphere of mass 10 kg rolls without slipping at 8.5 m/s. What percentage p of its total kinetic energy is rotational?

m = 10 kgv = 8.5 m/sI = (2/5)·m·r²
p = %
6.Hard
θ = 15°vs = 8.5 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 15° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 8.5 m along the slope.

θ = 15°s = 8.5 mI = (2/5)·m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 3.141 kg·m²
  2. 2. IO = 18.09 kg·m²
  3. 3. Pavg = 2.74 kW
  4. 4. v = 4.744 m/s
  5. 5. p = 28.57 %
  6. 6. v = 5.553 m/s

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