Download 6 Physics 111 HW16 - University of St. Thomas

Physics 111 HW16
Due Thursday, 30 June 2016
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AP01. A woman with mass 50 kg is standing on the rim of a large disk that is rotating at 0.50 rev/s about an axis
through its center and perpendicular to the disk. The disk has mass 110 kg and a radius 4.0 m. Calculate the
magnitude of the total angular momentum of the woman-plus-disk system. Assume you can treat the woman as
a point.
15 cm
AP02. A 1 kg ball travels in a straight line with speed
as shown in the figure at right. Calculate (using L =
r × p) the angular momentum of the ball about point
O in the three places (a, b, and c) indicated.
10 cm
12.0 m/s
a
c
b
10 cm
O
AP03. Under some circumstances, a star can collapse
into an extremely dense object made mostly of neutrons and called a neutron star. The density of a neutron star
is roughly 1014 times as great as that of ordinary solid matter. Suppose we represent the star as a uniform, solid,
rigid sphere, both before and after the collapse. The star’s initial radius was 7.0  105 km (comparable to our
sun); its final radius is 16 km. If the original star rotated once in 30 days, find the angular speed of the neutron
star.
AP04. Two uniform solid disks spin frictionlessly on the same spindle as shown
in the diagram at right. The top disk has a radius of 0.050 m and a mass of 1 kg.
The bottom disk has a radius of 0.080 m and a mass of 4 kg. Their initial angular
velocities are as shown. They collide and stick together. Find the final angular
velocity of the two as they rotate together, and show that kinetic energy was lost
during the collision.
ωt = 10 rev/s
ωb = 1 rev/s
AP06. A solid wood door 1.00 m wide and 2.00 m high is hinged along one side and has a total mass of 40.0 kg.
Initially open and at rest, the door is struck at its center by a handful of sticky mud with mass 0.500 kg, traveling
perpendicular to the door at 12.0 m/s just before impact. Find the final angular speed of the door. Does the mud
make a significant contribution to the moment of inertia?
 “Collision in Space!” A lightweight uniform rod 2m-long and mass
4kg is at rest in deep space nowhere near any sources of gravity. A
1 kg ball of sticky gum traveling at 10 m/s in a direction
perpendicular to the rod strikes the end of the rod and sticks to it.
After the gum sticks, the rod/gum will spin and move to the right.
a) Determine the location of the axis the rod/gum spins around.
b) What is the final angular speed of the rod/gum system?
c) What is the center of mass (translational) velocity of the rod/gum
system after the collision?
M = 4 kg
L = 2m
m = 1 kg
v = 10 m/s