ROTATIONAL MOTION 2
- A horizontal disc rotating freely about a vertical axis makes 90 revolutions per minute. An object of mass 20g falls vertically onto the disc and sticks to it at a distance of 50mm from the axis of rotation. If the speed of rotation is reduced to 80rpm, find the moment of inertia of the disc.
- The diagram shows a cylindrical drum of moment of inertia 0.50kgm2 and radius 20cm, which is free to rotate about an axle through the axis as shown. A string of length 8.8m is wound around the drum and pulled with a constant force of 10N.
Calculate,
(a) the torque on the drum
(b) its angular acceleration
If the drum was initially at rest, find
(c) its angular displacement when the string comes off
(d) the time that elapses before the string comes off
(e) the maximum angular velocity.
- A solid cylinder of mass 2.0kg and radius 10cm is set spinning and held just above a plane slope as shown.
The cylinder is then released so that it touches the slope at the bottom and starts to roll up it.
(a) Calculate the rotational kinetic energy of the cylinder before it is released.
(b) Describe the energy changes that take place from the moment the cylinder is released until it momentarily comes to rest at the top of the slope.
(c) How far does the cylinder travel along the slope before changing direction?
(d) Explain why in practice the actual distance travelled is less than this.
