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 = 1.4 m1.65 m5 kg3.5 kg

A pendulum is made of a uniform slender rod (5 kg, 1.4 m long) pivoted at its top end O, with a thin solid disc of mass 3.5 kg and radius 0.25 m fixed to its lower end. The disc swings in its own plane and its centre is 1.65 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 5 kgL = 1.4 mmdisc = 3.5 kgr = 0.25 md = 1.65 m
IO = kg·m²
2.Easy
k = 0.25 mn = 1200 rpm90 kg

A flywheel of mass 90 kg has a radius of gyration of 0.25 m about its axis. It spins at 1200 rpm. Find its kinetic energy Ek in kJ.

M = 90 kgk = 0.25 mn = 1200 rpm
Ek = kJ
3.Medium
L = 0.7 mm = 7.5 kgα

A uniform slender rod of mass 7.5 kg and length 0.7 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 = 7.5 kgL = 0.7 mg = 9.81 m/s²
atip = m/s²
4.Medium
L = 1.6 mm = 5 kgα

A uniform slender rod of mass 5 kg and length 1.6 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find the vertical force R that the pin exerts on the rod just after release.

m = 5 kgL = 1.6 mg = 9.81 m/s²
R = N
5.Hard
θ = 20°vs = 9.5 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 20° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 9.5 m along the slope.

θ = 20°s = 9.5 mI = (2/5)·m·r²g = 9.81 m/s²
v = m/s
6.Hard
300 m/s45 g0.42 mL = 0.8 m9 kgφ

A uniform slender rod of mass 9 kg and length 0.8 m hangs at rest from a frictionless pivot at its top end. A 45 g bullet moving horizontally at 300 m/s hits the rod 0.42 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 = 9 kgL = 0.8 mm = 45 gv = 300 m/sd = 0.42 mg = 9.81 m/s²
φ = °

Answer key

  1. 1. IO = 12.9 kg·m²
  2. 2. Ek = 44.41 kJ
  3. 3. atip = 14.71 m/s²
  4. 4. R = 12.26 N
  5. 5. v = 6.748 m/s
  6. 6. φ = 40.08 °

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