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 = 1.1 m1.2 m1.5 kg9.5 kg

A pendulum is made of a uniform slender rod (1.5 kg, 1.1 m long) pivoted at its top end O, with a thin solid disc of mass 9.5 kg and radius 0.1 m fixed to its lower end. The disc swings in its own plane and its centre is 1.2 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 1.5 kgL = 1.1 mmdisc = 9.5 kgr = 0.1 md = 1.2 m
IO = kg·m²
2.Easy
k = 0.6 m800 → 1700 rpm170 kg

A flywheel of mass 170 kg with a radius of gyration of 0.6 m is accelerated uniformly from 800 rpm to 1700 rpm. This takes 22 s. Ignoring friction, find the constant torque T needed.

m = 170 kgk = 0.6 mn1 = 800 rpmn2 = 1700 rpmt = 22 s
T = N·m
3.Medium
L = 1.8 mm = 17.5 kgα

A uniform slender rod of mass 17.5 kg and length 1.8 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 = 17.5 kgL = 1.8 mg = 9.81 m/s²
atip = m/s²
4.Medium
ω = ?L = 1 mm = 2 kg

A uniform slender rod of mass 2 kg and length 1 m is pinned at one end and released from rest in a horizontal position. 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 = 2 kgL = 1 mg = 9.81 m/s²
ω = rad/s
5.Hard
θ = 15°a

A solid sphere rolls without slipping down a slope inclined at 15° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 15°I = (2/5)·m·r²g = 9.81 m/s²
a = m/s²
6.Hard
200 m/s35 g0.98 mL = 1.2 m4 kgφ

A uniform slender rod of mass 4 kg and length 1.2 m hangs at rest from a frictionless pivot at its top end. A 35 g bullet moving horizontally at 200 m/s hits the rod 0.98 m below the pivot and stays embedded. Use g = 9.81 m/s². Find the largest angle φ from the vertical through which the rod swings.

M = 4 kgL = 1.2 mm = 35 gv = 200 m/sd = 0.98 mg = 9.81 m/s²
φ = °

Answer key

  1. 1. IO = 14.33 kg·m²
  2. 2. T = 262.2 N·m
  3. 3. atip = 14.71 m/s²
  4. 4. ω = 5.425 rad/s
  5. 5. a = 1.814 m/s²
  6. 6. φ = 60.29 °

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