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
k = 0.45 m1000 → 2400 rpm120 kg

A flywheel of mass 120 kg with a radius of gyration of 0.45 m is accelerated uniformly from 1000 rpm to 2400 rpm. The driving torque is a constant 210 N·m and friction can be ignored. How long t does this take?

m = 120 kgk = 0.45 mn1 = 1000 rpmn2 = 2400 rpmT = 210 N·m
t = s
2.Easy
Or = 0.15 mL = 1.3 m1.45 m2.5 kg3.5 kg

A pendulum is made of a uniform slender rod (2.5 kg, 1.3 m long) pivoted at its top end O, with a thin solid disc of mass 3.5 kg and radius 0.15 m fixed to its lower end. The disc swings in its own plane and its centre is 1.45 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 2.5 kgL = 1.3 mmdisc = 3.5 kgr = 0.15 md = 1.45 m
IO = kg·m²
3.Medium
L = 0.9 mm = 5.5 kgα

A uniform slender rod of mass 5.5 kg and length 0.9 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 = 5.5 kgL = 0.9 mg = 9.81 m/s²
R = N
4.Medium
v = ?L = 0.9 mm = 5 kg

A uniform slender rod of mass 5 kg and length 0.9 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 = 5 kgL = 0.9 mg = 9.81 m/s²
v = m/s
5.Hard
3.5 m/sω

A solid cylinder of mass 16.5 kg rolls without slipping at 3.5 m/s. What percentage p of its total kinetic energy is rotational?

m = 16.5 kgv = 3.5 m/sI = ½·m·r²
p = %
6.Hard
θ = 25°vs = 9.5 m

A thin hoop 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 9.5 m along the slope.

θ = 25°s = 9.5 mI = m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. t = 16.96 s
  2. 2. IO = 8.806 kg·m²
  3. 3. R = 13.49 N
  4. 4. v = 5.147 m/s
  5. 5. p = 33.33 %
  6. 6. v = 6.276 m/s

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