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 = 0.25 mL = 0.5 m0.75 m0.5 kg1 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 solid sphere of mass 1 kg and radius 0.25 m fixed to its lower end. The centre of the sphere is 0.75 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 0.5 mmsphere = 1 kgr = 0.25 md = 0.75 m
IO = kg·m²
2.Easy
Or = 0.15 mL = 1 m1.15 m2.5 kg5 kg

A pendulum is made of a uniform slender rod (2.5 kg, 1 m long) pivoted at its top end O, with a solid sphere of mass 5 kg and radius 0.15 m fixed to its lower end. The centre of the sphere is 1.15 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 2.5 kgL = 1 mmsphere = 5 kgr = 0.15 md = 1.15 m
IO = kg·m²
3.Medium
v = ?4.5 kgL = 2.5 mm = 7.5 kg

A uniform slender rod of mass 7.5 kg and length 2.5 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 4.5 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 = 7.5 kgL = 2.5 mmball = 4.5 kgg = 9.81 m/s²
v = m/s
4.Medium
n = 1300 rpmP = 28 kW

A shaft transmits 28 kW at 1300 rpm. Find the torque T in the shaft.

P = 28 kWn = 1300 rpm
T = N·m
5.Hard
0.9 m0.15 mn1​ = 50 rpm

A person stands on a frictionless turntable and holds a 1 kg dumbbell in each hand, 0.9 m from the axis. The person and turntable alone have a moment of inertia of 3.5 kg·m² about the axis. They turn at 50 rpm, then pull the dumbbells in to 0.15 m from the axis. Treat the dumbbells as point masses. Find the new speed n2 in rpm.

I0 = 3.5 kg·m²m = 2 × 1 kgr1 = 0.9 mr2 = 0.15 mn1 = 50 rpm
n2 = rpm
6.Hard
9.5 m/sω

A solid sphere of mass 14.5 kg rolls without slipping at 9.5 m/s. Find its total kinetic energy Ek.

m = 14.5 kgv = 9.5 m/sI = (2/5)·m·r²
Ek = J

Answer key

  1. 1. IO = 0.6292 kg·m²
  2. 2. IO = 7.491 kg·m²
  3. 3. v = 7.603 m/s
  4. 4. T = 205.7 N·m
  5. 5. n2 = 72.21 rpm
  6. 6. Ek = 916 J

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