A charge is released from rest in E and B fields. Both fields point along the x axis. Which of the following statements regarding the charge's motion are correct? y after the switch is closed?
6
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Captain Jirk reports to headquarters that he left the planet Senesca 1.88 × 10^4 seconds earlier. Headquarters sends back the message: "Was that spaceship proper time?" It will be spaceship proper time if it was
a. measured by one clock fixed at one spot on Senesca. b. measured by one clock fixed at one spot on the spaceship. c. measured by a clock on Senesca at departure and by a clock on the spaceship when reporting. d. measured by a clock on the spaceship when departing and by a clock on Senesca when reporting. e. calculated by dividing the distance from Senesca according to Senesca by the speed of the spaceship.
A frozen-food company freezes its spinach by first compressing it into large slabs and then exposing the slab of spinach to a low-temperature cooling medium. The large slab of compressed spinach is initially at a uniform temperature of 21°C; it must be reduced to an average temperature over the entire slab of –34°C. The temperature at any part of the slab, however, must never drop below –51°C. The cooling medium which passes across both sides of the slab is at a constant temperature of –90°C. The following data may be used for the spinach: density = 80 kg/m3; thermal conductivity = 0.87 W/(m K); specific heat = 2100 J/(kg K). Present a detailed analysis outlining a method estimate the maximum thickness of the slab of spinach that can be safely cooled in 60 min.
GIVEN
• Large slabs of spinach are exposed to a low-temperature cooling medium
• Initial uniform temperature (To) = 21°C
• Average temperature must be reduced to –34°C
• The temperature at any part must never drop below –51°C
• Cooling medium temperature (T?) = –90°C
• Density of spinach (?) = 80 kg/m3
• Thermal conductivity (k) = 0.87 W/(m K)
• Specific heat (c) = 2100 J/(kg K)
FIND
• Present a detailed analysis outlining a method to estimate the maximum thickness of the slab of spinach that can be safely cooled in 60 min
ASSUMPTIONS
• One dimensional conduction through the slab
• Constant and uniform thermal
properties
• The average temperature within the slab is equal to the average of the center and surface temperatures
SKETCH
_____ is proposed dark matter made up of particles other than protons and neutrons
A) Baryonic matter B) Biotic matter C) Nonbaryonic matter D) Abiotic matter
A 2.5-kg object falls vertically downward in a viscous medium at a constant speed of 2.5 m/s. How much work is done by the force the viscous medium exerts on the object as it falls 80 cm?
a. +2.0 J b. +20 J c. ?2.0 J d. ?20 J e. +40 J