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 = 0.1 mL = 1.3 m1.4 m1.5 kg8.5 kg

A pendulum is made of a uniform slender rod (1.5 kg, 1.3 m long) pivoted at its top end O, with a thin solid disc of mass 8.5 kg and radius 0.1 m fixed to its lower end. The disc swings in its own plane and its centre is 1.4 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 1.5 kgL = 1.3 mmdisc = 8.5 kgr = 0.1 md = 1.4 m
IO = kg·m²
2.Easy
L = 2.2 mGOd = 0.35 mm = 7.5 kg

A uniform slender rod of mass 7.5 kg and length 2.2 m rotates about an axis O perpendicular to the rod, 0.35 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 7.5 kgL = 2.2 md = 0.35 m
IO = kg·m²
3.Medium
12.5 kgaαM = 16.5 kgR = 0.2 m

A 12.5 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 16.5 kg and radius 0.2 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 2.5 m.

m = 12.5 kgM = 16.5 kgR = 0.2 mg = 9.81 m/s²h = 2.5 m
v = m/s
4.Medium
L = 1.6 mm = 4 kgα

A uniform slender rod of mass 4 kg and length 1.6 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find the acceleration atip of the free end just after release.

m = 4 kgL = 1.6 mg = 9.81 m/s²
atip = m/s²
5.Hard
4 m/sω

A solid sphere of mass 17 kg rolls without slipping at 4 m/s. Find its rotational kinetic energy Erot.

m = 17 kgv = 4 m/sI = (2/5)·m·r²
Erot = J
6.Hard
500 m/s45 g0.87 mL = 1.3 m8 kg

A uniform slender rod of mass 8 kg and length 1.3 m hangs at rest from a frictionless pivot at its top end. A 45 g bullet moving horizontally at 500 m/s hits the rod 0.87 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 8 kgL = 1.3 mm = 45 gv = 500 m/sd = 0.87 m
ω = rad/s

Answer key

  1. 1. IO = 17.55 kg·m²
  2. 2. IO = 3.944 kg·m²
  3. 3. v = 5.436 m/s
  4. 4. atip = 14.71 m/s²
  5. 5. Erot = 54.4 J
  6. 6. ω = 4.311 rad/s

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