Which are the two most popular candidates for gamma-ray bursters?
A) collisions between a white dwarf and a giant, and merger of two neutron stars
B) hypernova making a black hole, and merger of two neutron stars
C) formation of uranium in the core of a supergiant, and collisions of white dwarfs
D) mergers of two black holes, and merger of a neutron star and a white dwarf
E) hypernova making pulsars, and mergers of two white dwarfs
B
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Mass on a Spring: A 3.7-kg block on a horizontal frictionless surface is attached to an ideal spring whose force constant (spring constant) is 450 N/m. The block is pulled from its equilibrium position at x = 0.000 m to a position x = +0.080 m and is released from rest. The block then executes simple harmonic motion along the horizontal x-axis. The maximum elastic potential energy of the system is closest to
A. 1.4 J. B. 1.3 J. C. 1.6 J. D. 1.7 J. E. 1.8 J.
In beauty salons and in homes, a ubiquitous device is a hair dryer. The front end of the typical hair dryer is idealized as a thin walled cylindrical duct with a 6-cm diameter with a fan at the inlet that blows air over an electric heating coil as schematically shown in the figure. The design of the appliance requires two power settings, with which the air blown over the electric heating coil is heated from the ambient temperature of 220C to an outlet temperature of 440C and with exit air velocities of 1.0 m/s and 1.5 m/s. Estimate the electric power required for the heating coil to meet these conditions, assuming that the heat loss from the outside of the dryer duct is neglected.
GIVEN - Dryer idealized as cylindrical duct of d= 6 cm =0.06 m with 2 power settings - Air blown over coil is heated from T?=220C to outlet temp Tf=440C with exit air velocities (a) 1.0 m/s and (b) 1.5 m/s. FIND - Electric power required for heating coil to meet these condition. ASSUMPTIONS - Steady state conditions prevail - Heat loss from outside of dryer duct is neglected. PROPERTIES AND CONSTANTS The air properties at 300 K are Density of air (?)=1.177 kg/m3 Specific heat capacity(Cp)= 1.0049 kJ/kgK
A deuterium nucleus and a tritium nucleus react to yield one alpha particle, a neutron, and energy. For this reaction, the sum of the masses of reaction products after the reaction is ________ the sum of the masses of particles before the reaction.
A. greater than B. equal to C. less than