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
k = 0.25 m0 → 800 rpm40 kg

A flywheel of mass 40 kg with a radius of gyration of 0.25 m is accelerated uniformly from rest to 800 rpm. The driving torque is a constant 52 N·m and friction can be ignored. How long t does this take?

m = 40 kgk = 0.25 mn1 = 0 rpmn2 = 800 rpmT = 52 N·m
t = s
2.Easy
k = 0.5 m0 → 1200 rpm170 kg

A flywheel of mass 170 kg with a radius of gyration of 0.5 m is accelerated uniformly from rest to 1200 rpm. This takes 17 s. Ignoring friction, find the constant torque T needed.

m = 170 kgk = 0.5 mn1 = 0 rpmn2 = 1200 rpmt = 17 s
T = N·m
3.Medium
L = 2.2 mm = 17.5 kgα

A uniform slender rod of mass 17.5 kg and length 2.2 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 = 2.2 mg = 9.81 m/s²
atip = m/s²
4.Medium
ω = ?3.5 kgL = 1.8 mm = 10 kg

A uniform slender rod of mass 10 kg and length 1.8 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 3.5 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 = 1.8 mmball = 3.5 kgg = 9.81 m/s²
ω = rad/s
5.Hard
280 m/s50 g0.3 mL = 0.5 m10 kg

A uniform slender rod of mass 10 kg and length 0.5 m hangs at rest from a frictionless pivot at its top end. A 50 g bullet moving horizontally at 280 m/s hits the rod 0.3 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 10 kgL = 0.5 mm = 50 gv = 280 m/sd = 0.3 m
ω = rad/s
6.Hard
θ = 20°a

A hollow sphere rolls without slipping down a slope inclined at 20° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 20°I = (2/3)·m·r²g = 9.81 m/s²
a = m/s²

Answer key

  1. 1. t = 4.028 s
  2. 2. T = 314.2 N·m
  3. 3. atip = 14.71 m/s²
  4. 4. ω = 3.682 rad/s
  5. 5. ω = 5.013 rad/s
  6. 6. a = 2.013 m/s²

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