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 = 0.05 mL = 0.8 m0.85 m1.5 kg6 kg

A pendulum is made of a uniform slender rod (1.5 kg, 0.8 m long) pivoted at its top end O, with a solid sphere of mass 6 kg and radius 0.05 m fixed to its lower end. The centre of the sphere is 0.85 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 1.5 kgL = 0.8 mmsphere = 6 kgr = 0.05 md = 0.85 m
IO = kg·m²
2.Easy
k = 0.35 m0 → 1400 rpm170 kg

A flywheel of mass 170 kg with a radius of gyration of 0.35 m is accelerated uniformly from rest to 1400 rpm. The driving torque is a constant 130 N·m and friction can be ignored. How long t does this take?

m = 170 kgk = 0.35 mn1 = 0 rpmn2 = 1400 rpmT = 130 N·m
t = s
3.Medium
n = 2600 rpmP = 27 kW

A shaft transmits 27 kW at 2600 rpm. Find the torque T in the shaft.

P = 27 kWn = 2600 rpm
T = N·m
4.Medium
ω = ?L = 2.3 mm = 2.5 kg

A uniform slender rod of mass 2.5 kg and length 2.3 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 = 2.5 kgL = 2.3 mg = 9.81 m/s²
ω = rad/s
5.Hard
θ = 15°vs = 9.5 m

A solid cylinder starts from rest and rolls without slipping down a slope inclined at 15° to the horizontal. Use g = 9.81 m/s². Its radius is 0.4 m. Find its angular velocity ω after it has rolled 9.5 m along the slope.

θ = 15°s = 9.5 mI = ½·m·r²g = 9.81 m/s²r = 0.4 m
ω = rad/s
6.Hard
θ = 20°as = 4 m

A hollow sphere rolls without slipping down a slope inclined at 20° to the horizontal. Use g = 9.81 m/s². It starts from rest. How long t does it take to roll 4 m down the slope?

θ = 20°I = (2/3)·m·r²g = 9.81 m/s²s = 4 m
t = s

Answer key

  1. 1. IO = 4.661 kg·m²
  2. 2. t = 23.49 s
  3. 3. T = 99.17 N·m
  4. 4. ω = 3.577 rad/s
  5. 5. ω = 14.18 rad/s
  6. 6. t = 1.993 s

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