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 = 1.3 m1.55 m0.5 kg8 kg

A pendulum is made of a uniform slender rod (0.5 kg, 1.3 m long) pivoted at its top end O, with a solid sphere of mass 8 kg and radius 0.25 m fixed to its lower end. The centre of the sphere is 1.55 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 1.3 mmsphere = 8 kgr = 0.25 md = 1.55 m
IO = kg·m²
2.Easy
k = 0.35 mn = 2400 rpm190 kg

A flywheel of mass 190 kg has a radius of gyration of 0.35 m about its axis. It spins at 2400 rpm. Find its kinetic energy Ek in kJ.

M = 190 kgk = 0.35 mn = 2400 rpm
Ek = kJ
3.Medium
v = ?4 kgL = 1.7 mm = 5 kg

A uniform slender rod of mass 5 kg and length 1.7 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 4 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 = 5 kgL = 1.7 mmball = 4 kgg = 9.81 m/s²
v = m/s
4.Medium
n = 2700 rpmT = 140 N·m

A motor delivers a torque of 140 N·m at 2700 rpm. Find its power output P in kW.

T = 140 N·mn = 2700 rpm
P = kW
5.Hard
θ = 30°as = 6 m

A solid sphere rolls without slipping down a slope inclined at 30° to the horizontal. Use g = 9.81 m/s². It starts from rest. How long t does it take to roll 6 m down the slope?

θ = 30°I = (2/5)·m·r²g = 9.81 m/s²s = 6 m
t = s
6.Hard
220 m/s45 g0.34 mL = 0.6 m6.5 kgφ

A uniform slender rod of mass 6.5 kg and length 0.6 m hangs at rest from a frictionless pivot at its top end. A 45 g bullet moving horizontally at 220 m/s hits the rod 0.34 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 = 6.5 kgL = 0.6 mm = 45 gv = 220 m/sd = 0.34 mg = 9.81 m/s²
φ = °

Answer key

  1. 1. IO = 19.7 kg·m²
  2. 2. Ek = 735.1 kJ
  3. 3. v = 6.185 m/s
  4. 4. P = 39.58 kW
  5. 5. t = 1.851 s
  6. 6. φ = 51.26 °

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