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 = 0.6 m0.75 m1.5 kg1.5 kg

A pendulum is made of a uniform slender rod (1.5 kg, 0.6 m long) pivoted at its top end O, with a thin solid disc of mass 1.5 kg and radius 0.15 m fixed to its lower end. The disc swings in its own plane and its centre is 0.75 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 1.5 kgL = 0.6 mmdisc = 1.5 kgr = 0.15 md = 0.75 m
IO = kg·m²
2.Easy
L = 1.1 mGOd = 0.15 mm = 8 kg

A uniform slender rod of mass 8 kg and length 1.1 m rotates about an axis O perpendicular to the rod, 0.15 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 8 kgL = 1.1 md = 0.15 m
IO = kg·m²
3.Medium
ω = ?5 kgL = 2.1 mm = 6.5 kg

A uniform slender rod of mass 6.5 kg and length 2.1 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 5 kg is fixed to its free end. 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 = 6.5 kgL = 2.1 mmball = 5 kgg = 9.81 m/s²
ω = rad/s
4.Medium
v = ?3 kgL = 1 mm = 10 kg

A uniform slender rod of mass 10 kg and length 1 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 3 kg is fixed to its free end. Ignore friction and use g = 9.81 m/s². Find the speed v of the free end as the rod swings through the vertical position.

m = 10 kgL = 1 mmball = 3 kgg = 9.81 m/s²
v = m/s
5.Hard
θ = 15°a

A solid cylinder rolls without slipping down a slope inclined at 15° to the horizontal. Use g = 9.81 m/s². Find the smallest coefficient of static friction μs that prevents it from slipping.

θ = 15°I = ½·m·r²g = 9.81 m/s²
μs =
6.Hard
8 m/sω

A solid cylinder of mass 12 kg rolls without slipping at 8 m/s. Find its rotational kinetic energy Erot.

m = 12 kgv = 8 m/sI = ½·m·r²
Erot = J

Answer key

  1. 1. IO = 1.041 kg·m²
  2. 2. IO = 0.9867 kg·m²
  3. 3. ω = 3.28 rad/s
  4. 4. v = 4.978 m/s
  5. 5. μs = 0.08932
  6. 6. Erot = 192 J

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