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 = 1.5 m1.75 m4 kg5 kg

A pendulum is made of a uniform slender rod (4 kg, 1.5 m long) pivoted at its top end O, with a thin solid disc of mass 5 kg and radius 0.25 m fixed to its lower end. The disc swings in its own plane and its centre is 1.75 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 4 kgL = 1.5 mmdisc = 5 kgr = 0.25 md = 1.75 m
IO = kg·m²
2.Easy
L = 1.2 mGOd = 0.45 mm = 7 kg

A uniform slender rod of mass 7 kg and length 1.2 m rotates about an axis O perpendicular to the rod, 0.45 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 7 kgL = 1.2 md = 0.45 m
IO = kg·m²
3.Medium
11 kgaαM = 9 kgR = 0.4 m

An 11 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 9 kg and radius 0.4 m that turns on a frictionless horizontal axle. The block is released from rest. Use g = 9.81 m/s². Find the tension T in the cord.

m = 11 kgM = 9 kgR = 0.4 mg = 9.81 m/s²
T = N
4.Medium
n = 2200 rpmT = 1100 N·m

A motor delivers a torque of 1100 N·m at 2200 rpm. Find its power output P in kW.

T = 1100 N·mn = 2200 rpm
P = kW
5.Hard
θ = 10°vs = 1 m

A solid cylinder starts from rest and rolls without slipping down a slope inclined at 10° to the horizontal. Use g = 9.81 m/s². Its radius is 0.1 m. Find its angular velocity ω after it has rolled 1 m along the slope.

θ = 10°s = 1 mI = ½·m·r²g = 9.81 m/s²r = 0.1 m
ω = rad/s
6.Hard
9 m/sω

A solid sphere of mass 4.5 kg rolls without slipping at 9 m/s. What percentage p of its total kinetic energy is rotational?

m = 4.5 kgv = 9 m/sI = (2/5)·m·r²
p = %

Answer key

  1. 1. IO = 18.47 kg·m²
  2. 2. IO = 2.257 kg·m²
  3. 3. T = 31.33 N
  4. 4. P = 253.4 kW
  5. 5. ω = 15.07 rad/s
  6. 6. p = 28.57 %

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