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 = 0.1 mL = 1.5 m1.6 m0.5 kg9 kg

A pendulum is made of a uniform slender rod (0.5 kg, 1.5 m long) pivoted at its top end O, with a solid sphere of mass 9 kg and radius 0.1 m fixed to its lower end. The centre of the sphere is 1.6 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 1.5 mmsphere = 9 kgr = 0.1 md = 1.6 m
IO = kg·m²
2.Easy
k = 0.6 m0 → 1100 rpm40 kg

A flywheel of mass 40 kg with a radius of gyration of 0.6 m is accelerated uniformly from rest to 1100 rpm. This takes 17 s. Ignoring friction, find the constant torque T needed.

m = 40 kgk = 0.6 mn1 = 0 rpmn2 = 1100 rpmt = 17 s
T = N·m
3.Medium
v = ?L = 2 mm = 9 kg

A uniform slender rod of mass 9 kg and length 2 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 speed v of the free end as the rod swings through the vertical position.

m = 9 kgL = 2 mg = 9.81 m/s²
v = m/s
4.Medium
n = 2200 rpmT = 1610 N·m

A motor delivers a torque of 1610 N·m at 2200 rpm. Find its power output P in kW.

T = 1610 N·mn = 2200 rpm
P = kW
5.Hard
disc: 39 kgring: 6 kgn1​ = 100 rpm

A uniform solid disc (mass 39 kg, radius 0.5 m) spins freely at 100 rpm about a vertical frictionless shaft. A thin ring of mass 6 kg and the same radius is dropped onto it from rest, centred on the shaft, and the two quickly spin together. How much kinetic energy ΔE is lost in the process?

Mdisc = 39 kgMring = 6 kgR = 0.5 mn1 = 100 rpm
ΔE = J
6.Hard
θ = 35°vs = 1 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 35° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 1 m along the slope.

θ = 35°s = 1 mI = (2/5)·m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 23.45 kg·m²
  2. 2. T = 97.57 N·m
  3. 3. v = 7.672 m/s
  4. 4. P = 370.9 kW
  5. 5. ΔE = 62.89 J
  6. 6. v = 2.835 m/s

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