Angular Momentum: A solid, uniform, horizontal disk with a diameter of 2.0 m and a mass of 4.0 kg freely rotates at 36 rpm about a vertical axis through its center. A small 0.50-kg stone is suddenly dropped onto the disk and sticks to the disk at a distance of 80 cm from the axis of rotation. The figure shows before and after views.(a) Before the stone fell, what was the moment of inertia of the disk about its central axis?(b) After the stone stuck, what was the moment of inertia of the system about the same axis?(c) What is the angular velocity of the disk (in rpm) after the stone fell onto the disk?
What will be an ideal response?
(a) 2.0 kg ? m2 (b) 2.3 kg ? m2 (c) 31 rpm
You might also like to view...
The word LASER is an acronym for
A) Light Altered Spectra of Energy Radiated. B) Latent Source of Enhanced Radiation. C) Light Amplification by the Stimulated Emission of Radiation. D) Light Absorbed States of Energetic Resonance. E) none of the above answers.
In designing buildings to be erected in an area prone to earthquakes, what relationship should the designer try to achieve between the natural frequencies of the building and the typical earthquake frequencies?
What will be an ideal response?
Light-emitting diodes or LEDs are currently perhaps the most energy-efficient lighting systems. Finned surface heat sinks are used to cool high-intensity LED lighting that are used for spot and/or track lighting systems. A typical circular pin-fin heat sink is shown in the figure, and it is desirable that the fin-base temperature be less than 115°C to ensure efficient performance and longer life of the LED lamp. The fins are made of cold-forged, high-conductivity aluminum (k = 210 W/m K). Each pin has a diameter of 4 mm and a length of 40 mm. If the surrounding air is at 22°C, and it has a convection heat transfer coefficient of ch = 10 W/(m2 K), determine the temperature distribution in the fin, considering convection from the fin tip and the heat transfer rate from the fin. Model it
as a one-dimensional system, use a minimum of 9 nodes (including the ones at the base and tip) or more in your numerical scheme, and determine the effect of extra nodes. Compare the results with the one-dimensional fin analysis of Chapter 2. Also, if 90 such fins are evenly distributed on a 50-mm-diameter circular base, what is the maximum heat transfer rate that is dissipated by this heat sink so that the base temperature is less than 115°C? In a typical LED lamp, approximately 70% of the electric power (or wattage) is dissipated as heat (the remainder 30% is useful light). Determine the maximum power of the lamp, in watts, for which this heat sink is used.
GIVEN
• Light emitting diodes
• Fin base temperature (T0)= 1150C
• Surrounding air temperature (T?)= 220C
• Convection heat transfer coefficient ( ch )= 10 W/(m2 K)
• Thermal conductivity (k)=210 W/(m K)
• Fin diameter (d)= 4 mm = 0.004 m
• Fin length (L)= 40 mm =0.04 m
• Number of nodes (N)=9
FIND (a) Temperature distribution in the fin considering convection from fin tip
(b) Heat transfer rate from the fin.
(c) Maximum heat transfer rate dissipated by 90 such evenly distributed fins
(d) Maximum power of lamp in watts.
SKETCH
In a paramagnetic material if a large magnetic filed is first applied and then reduced to zero, the intensity of magnetization is then equal to _________.
Fill in the blank(s) with the appropriate word(s).