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 m3.5 kg6.5 kg

A pendulum is made of a uniform slender rod (3.5 kg, 0.5 m long) pivoted at its top end O, with a solid sphere of mass 6.5 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 = 3.5 kgL = 0.5 mmsphere = 6.5 kgr = 0.25 md = 0.75 m
IO = kg·m²
2.Easy
k = 0.15 m200 → 1900 rpm200 kg

A flywheel of mass 200 kg with a radius of gyration of 0.15 m is accelerated uniformly from 200 rpm to 1900 rpm. The driving torque is a constant 53 N·m and friction can be ignored. How long t does this take?

m = 200 kgk = 0.15 mn1 = 200 rpmn2 = 1900 rpmT = 53 N·m
t = s
3.Medium
L = 1.4 mm = 16.5 kgα

A uniform slender rod of mass 16.5 kg and length 1.4 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 = 16.5 kgL = 1.4 mg = 9.81 m/s²
R = N
4.Medium
L = 3 mm = 3 kgα

A uniform slender rod of mass 3 kg and length 3 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find its angular acceleration α just after release.

m = 3 kgL = 3 mg = 9.81 m/s²
α = rad/s²
5.Hard
θ = 25°vs = 10 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 25° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 10 m along the slope.

θ = 25°s = 10 mI = (2/5)·m·r²g = 9.81 m/s²
v = m/s
6.Hard
160 m/s30 g0.4 mL = 0.5 m2 kg

A uniform slender rod of mass 2 kg and length 0.5 m hangs at rest from a frictionless pivot at its top end. A 30 g bullet moving horizontally at 160 m/s hits the rod 0.4 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 2 kgL = 0.5 mm = 30 gv = 160 m/sd = 0.4 m
ω = rad/s

Answer key

  1. 1. IO = 4.11 kg·m²
  2. 2. t = 15.12 s
  3. 3. R = 40.47 N
  4. 4. α = 4.905 rad/s²
  5. 5. v = 7.696 m/s
  6. 6. ω = 11.2 rad/s

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