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 = 1.2 m1.35 m4 kg10 kg

A pendulum is made of a uniform slender rod (4 kg, 1.2 m long) pivoted at its top end O, with a solid sphere of mass 10 kg and radius 0.15 m fixed to its lower end. The centre of the sphere is 1.35 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 4 kgL = 1.2 mmsphere = 10 kgr = 0.15 md = 1.35 m
IO = kg·m²
2.Easy
L = 1.3 mGOd = 0.2 mm = 2 kg

A uniform slender rod of mass 2 kg and length 1.3 m rotates about an axis O perpendicular to the rod, 0.2 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 2 kgL = 1.3 md = 0.2 m
IO = kg·m²
3.Medium
13.5 kgaαM = 10 kgR = 0.35 m

A 13.5 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 10 kg and radius 0.35 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 = 13.5 kgM = 10 kgR = 0.35 mg = 9.81 m/s²
α = rad/s²
4.Medium
n = 1900 rpmTb​ = 170 N·mI = 12.5 kg·m²

A flywheel with a moment of inertia of 12.5 kg·m² spins at 1900 rpm. A brake applies a constant friction torque of 170 N·m. How long t does it take to stop?

I = 12.5 kg·m²n = 1900 rpmTb = 170 N·m
t = s
5.Hard
θ = 20°vs = 3.5 m

A hollow sphere starts from rest and rolls without slipping down a slope inclined at 20° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 3.5 m along the slope.

θ = 20°s = 3.5 mI = (2/3)·m·r²g = 9.81 m/s²
v = m/s
6.Hard
θ = 40°a

A hollow sphere rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 40°I = (2/3)·m·r²g = 9.81 m/s²
a = m/s²

Answer key

  1. 1. IO = 20.23 kg·m²
  2. 2. IO = 0.3617 kg·m²
  3. 3. α = 20.45 rad/s²
  4. 4. t = 14.63 s
  5. 5. v = 3.754 m/s
  6. 6. a = 3.783 m/s²

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