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 = 0.25 mL = 1 m1.25 m5 kg5.5 kg

A pendulum is made of a uniform slender rod (5 kg, 1 m long) pivoted at its top end O, with a thin solid disc of mass 5.5 kg and radius 0.25 m fixed to its lower end. The disc swings in its own plane and its centre is 1.25 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 5 kgL = 1 mmdisc = 5.5 kgr = 0.25 md = 1.25 m
IO = kg·m²
2.Easy
Or = 0.05 mL = 0.8 m0.85 m0.5 kg2 kg

A pendulum is made of a uniform slender rod (0.5 kg, 0.8 m long) pivoted at its top end O, with a solid sphere of mass 2 kg and radius 0.05 m fixed to its lower end. The centre of the sphere is 0.85 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 0.8 mmsphere = 2 kgr = 0.05 md = 0.85 m
IO = kg·m²
3.Medium
n = 1800 rpmTb​ = 25 N·mI = 19 kg·m²

A flywheel with a moment of inertia of 19 kg·m² spins at 1800 rpm. A brake applies a constant friction torque of 25 N·m. How many revolutions N does the flywheel make before it stops?

I = 19 kg·m²n = 1800 rpmTb = 25 N·m
N = rev
4.Medium
8.5 kgaαM = 18 kgR = 0.3 m

An 8.5 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 18 kg and radius 0.3 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 = 8.5 kgM = 18 kgR = 0.3 mg = 9.81 m/s²
a = m/s²
5.Hard
8 m/sω

A hollow sphere of mass 14 kg rolls without slipping at 8 m/s. Find its rotational kinetic energy Erot.

m = 14 kgv = 8 m/sI = (2/3)·m·r²
Erot = J
6.Hard
θ = 10°vs = 4.5 m

A thin hoop starts from rest and rolls without slipping down a slope inclined at 10° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 4.5 m along the slope.

θ = 10°s = 4.5 mI = m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 10.43 kg·m²
  2. 2. IO = 1.554 kg·m²
  3. 3. N = 2149 rev
  4. 4. a = 4.765 m/s²
  5. 5. Erot = 298.7 J
  6. 6. v = 2.769 m/s

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