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 = 0.2 mL = 1.1 m1.3 m0.5 kg4.5 kg

A pendulum is made of a uniform slender rod (0.5 kg, 1.1 m long) pivoted at its top end O, with a thin solid disc of mass 4.5 kg and radius 0.2 m fixed to its lower end. The disc swings in its own plane and its centre is 1.3 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 1.1 mmdisc = 4.5 kgr = 0.2 md = 1.3 m
IO = kg·m²
2.Easy
Or = 0.15 mL = 0.7 m0.85 m2 kg1.5 kg

A pendulum is made of a uniform slender rod (2 kg, 0.7 m long) pivoted at its top end O, with a solid sphere of mass 1.5 kg and radius 0.15 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 = 2 kgL = 0.7 mmsphere = 1.5 kgr = 0.15 md = 0.85 m
IO = kg·m²
3.Medium
ω = ?4 kgL = 0.6 mm = 10 kg

A uniform slender rod of mass 10 kg and length 0.6 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 4 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 = 10 kgL = 0.6 mmball = 4 kgg = 9.81 m/s²
ω = rad/s
4.Medium
n = 1400 rpmP = 18 kW

A shaft transmits 18 kW at 1400 rpm. Find the torque T in the shaft.

P = 18 kWn = 1400 rpm
T = N·m
5.Hard
8 m/sω

A thin hoop of mass 3.5 kg rolls without slipping at 8 m/s. What percentage p of its total kinetic energy is rotational?

m = 3.5 kgv = 8 m/sI = m·r²
p = %
6.Hard
θ = 15°vs = 7.5 m

A thin hoop 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 7.5 m along the slope.

θ = 15°s = 7.5 mI = m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 7.897 kg·m²
  2. 2. IO = 1.424 kg·m²
  3. 3. ω = 6.335 rad/s
  4. 4. T = 122.8 N·m
  5. 5. p = 50 %
  6. 6. v = 4.364 m/s

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