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| Q. A constant torque of
1.56 N-m is applied to a rotating solid disk of radius 15
cm and mass 5.71 kg. What is the angular velocity of the
disk after 10 seconds? A. Torque T = 1.56 Nm Radius r = 15 cm = 0.15 m Mass m = 5.71 kg Time t = 10 s
Initial angular velocity w0 of the disc is not given. We assume it to be zero. Final angular velocity of the disc = w = w0 + at where a is the angular acceleration and torque T = I a where I is the moment of inertia, which for a solid disc, about an axis passing through its center and perpendicular to it is = ½ mr2 hence I = ½ x 0.15 x 0.15 x 5.71 = 0.064 hence a = 1.56 / 0.064 = 24.28 and w = 24.28 x 10 = 242.8 rad/s Q. Find the moment of inertia of a drum shaped like a right circular cylinder of radius 0.156 m and mass 5.71 kg.
A. Moment of inertia I of a hollow cylinder about an axis passing through the center and perpendicular to its cross section is mr2. hence I = 5.71 x (0.156)2 = 0.14 kg m2 |
Q A string 1 meter long is used to whirl a . 50 kg. stone in a vertical circle. What is the tension in the string when the stone is at the top of the circle moving at 5.0m/s.
R = 1 m, m=0.50 kg, VH = 5 m/s
Tension at the highest point :
TH=(mvH2)/r- mg
= ((0.50 x 52 )/1) - 0.50 x 9.8
=12.5 – 4.9
=7.6 N.
An object is moving in a circle at a
constant speed. From this you know that there
a) is no net force acting on the object
b) is at least one force acting on the
object
c) are at least two forces acting on
the object, which balance each other
d) are at least two forces acting on
the object, which do not balance each other
e) must be more than two forces acting
on the object
If a net
torque is applied to a rigid object, that object will experience
which of the following?
a.
a constant angular
velocity
b. a constant angular momentum
c.
an increasing moment of
inertia
d. an angular acceleration
A figure
skater with arms initially extended starts spinning on the ice at
3 rad/s. After she then pulls her arms into her body, which of
the following results?
a smaller rotational rate
a greater rotational rate
a greater angular momentum
a smaller angular momentum
