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 = 0.5 m0.65 m0.5 kg6 kg

A pendulum is made of a uniform slender rod (0.5 kg, 0.5 m long) pivoted at its top end O, with a thin solid disc of mass 6 kg and radius 0.15 m fixed to its lower end. The disc swings in its own plane and its centre is 0.65 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 0.5 mmdisc = 6 kgr = 0.15 md = 0.65 m
IO = kg·m²
2.Easy
Or = 0.1 mL = 1.4 m1.5 m0.5 kg8.5 kg

A pendulum is made of a uniform slender rod (0.5 kg, 1.4 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 1.5 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 1.4 mmdisc = 8.5 kgr = 0.1 md = 1.5 m
IO = kg·m²
3.Medium
0 → 500 rpmI = 36.5 kg·m²

A motor brings a flywheel with a moment of inertia of 36.5 kg·m² from rest up to 500 rpm in 25 s. Ignoring losses, find the average power Pavg it delivers, in kW.

I = 36.5 kg·m²n = 500 rpmt = 25 s
Pavg = kW
4.Medium
v = ?5 kgL = 2.2 mm = 6.5 kg

A uniform slender rod of mass 6.5 kg and length 2.2 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 speed v of the free end as the rod swings through the vertical position.

m = 6.5 kgL = 2.2 mmball = 5 kgg = 9.81 m/s²
v = m/s
5.Hard
θ = 40°vs = 3 m

A solid cylinder starts from rest and rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 3 m along the slope.

θ = 40°s = 3 mI = ½·m·r²g = 9.81 m/s²
v = m/s
6.Hard
θ = 30°vs = 4.5 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 30° to the horizontal. Use g = 9.81 m/s². Its radius is 0.2 m. Find its angular velocity ω after it has rolled 4.5 m along the slope.

θ = 30°s = 4.5 mI = (2/5)·m·r²g = 9.81 m/s²r = 0.2 m
ω = rad/s

Answer key

  1. 1. IO = 2.644 kg·m²
  2. 2. IO = 19.49 kg·m²
  3. 3. Pavg = 2.001 kW
  4. 4. v = 7.049 m/s
  5. 5. v = 5.022 m/s
  6. 6. ω = 28.08 rad/s

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