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Fysica week 5
Terms in this set (17)
What is a rigid object?
An object with a shape that doesn't change, so that particles composing it stay in fixed positions relative to one another.
What are axis of rotation?
A line where the center of circle lie on.
What is R?
The distance between point or particle to the axis of rotation.
What does it means when an object makes one complete revolution?
That it has rotated 360° or 2π
When will an object rotates faster? Close tot axis of rotation or farther?
Objects farther away, because they have to cover more meters in the same time.
A carousel is initially at rest. At t= 0 it is given a constant angular acceleration α = 0.060 rad/s², which increases its angular velocity for 8.0 sec. At t = 8.0 sec, determine the magnitude of the following quanties: (a) the angular velocity of the carousel; (b) the linear velocity of a child located 2.5 m form the center; (c) the tangential acceleration of that child; (d) the centripetal acceleration of the child; and (e) the total linear acceleration of the child.
(a) ω₂ = ω₁ + α ∆t = 0 + (0.060)(8.0) = 0.48 rad/s
(b) v = Rω = (2.5)(0.48) = 1.2 m/s
(c) αtan = Rα = 0.15 m/s²
(d) αR = 0.58 m/s²
(e) a = 0.60 m/s²
What is frequency?
Number of complete revolutions (2π) per sec.
The platter of the hard drive of a computer rotates at 720 rpm (revolutions per min)
(a) What is the angular velocity of the platter?
(b) If the reading head of the drive is located 3.00 cm form the rotation axis, what is the linear speed of the point on the platter just below it?
(c) If a singel bit requires 0.50 µm of length along the direction of motion, how many bits per sed can the writing head write it it 3.00 cm from the axis?
(a) ω = 754 rad/s
(b) v = Rω = 22.6 m/s
(c) 45 x 10⁶ bits per second
A disk of R = 3.0 m rotates at an angular velocity w = (1.6 + 1.2t) rad/s, where t is in seconds. At the instant t = 2.0 s, determine (a) the angular acceleration, and (b) the speed v and the components of the acceleration of a point on the edge of the disk.
(a) α = 1.2 rad/s²
(b) v = 12.0 m/s
αtan = 3.6 m/s²
αR = 48 m/s²
A centrifuge rotor is accelerated from rest to 20,000 rpm in 30 sec.
(a) What is its average angular acceleration?
(b) Through how many revolutions has the centrifuge rotor turned during acceleration period, assuming constant angular acceleration?
(a) α = 70 rad/s² = 11 revolutions per sec.
(b) 5.0 x 10³ rev
What is the torque?
To make an object start rotating there is a force needed. How effective you're producing a rotation is called a torque
When do you have a bigger torque?
- If the arm is very large.
- If the direction of torque is 90° on axis of rotation
Two thin disk-shaped wheels, of Ra = 30 cm and Rb = 50 cm, are attachted to each other on an axle that passes through the center of each. Calculate the the net torque on this compound wheel due to the two forces shown, each of magnitude 50 N.
τ = -6.7 mN
Where does the rotational inertia (I) depends on?
- mass distribution, where object has a large diameter it also has greater rotational inertia
- location of the axis of rotation, when the mass is concentrated farther from the axis of rotation, the rotational inertia is greater.
Two small weight of mass 5.0 kg and 7.0 kg are mounted 4.0 m apart on a light rod (whose mass can be ignored). Calculate the moment of inertia of the system (a) when rotated about an axis halfway between the weights and (b) when rotated about an axis 0.50 to the left of the 5.0 kg mass.
(a) I = 48 kgm²
(b) I - 143 kgm²
A 15.0 N force is applied to a cord wrapped around a pulley of mass M = 4.00 kg and R0 = 33.0 cm. The pulley accelerates uniformly from rest to an angular speed of 30.0 rad/s in 3.00 s. If there is a frictional torque 1.10 mN at the axle, determine the moment of inertia of the pulley. The pulley rotates about it center.
I = 0.385 kgm²
Flywheels which are simple large rotating disk (I = 1/2 MR₀²) have been suggested as a means of storing energy for solar powered generating systems. Estimate the kinetic energy that can be stored in an 80.000 kg flywheel with a diameter of 10 m. Assume it could hold together at 100 rpm.
K = 5.5 x 10⁷ J
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