Questions asked by lisa

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• A puddle holds 150 g of water. If 0.50 g of water evaporates from the surface, what is the approximate temperature change of the remaining water? (Lv = 2259 × 10^3 J/kg)
  
• The filament temperature of a light bulb is 2 000 K when the bulb delivers 40 W of power. If its emissivity remains constant, what power is delivered when the filament temperature is 2 500 K?
  
• During each cycle of operation a refrigerator absorbs 55 cal from the freezer compartment and expels 85 cal to the room. If one cycle occurs every 10 s, how many minutes will it take to freeze 500 g of water, initially at 0°C? (Lv = 80 cal/g)
  
• On a multiple choice test with 20 questions, each question has four possible answers, one of which is correct. If 10 students sit for the test, what is the probability that one student does not get any correct answer at all?
  
• A long, narrow steel rod of length 2.5000 m at 25°C is oscillating as a pendulum about a horizontal axis through one end. If the temperature changes to 0°C, what will be the fractional change in its period?
  
• A 23.4kg solid aluminum cylindrical wheel of radius 0.41 m is rotating about its axle on frictionless bearings with angular velocity ω = 32.8 rad/s. If its temperature is now raised from 20.0oC to 75.0oC, what is the fractional change in ω?
  
• A hand pump is being used to inflate a bicycle tire that has a gauge pressure of 40.0 psi. If the pump is a cylinder of length 18.0 in. with a cross-sectional area of 3.00 in2. , how far down must the piston be pushed before air will flow into the tire?
  
• After a hot shower and dishwashing, there is "no hot water" left in the 50-gal (185 L) water heater. This suggests that the tank has emptied and refilled with water at roughly 10°C a) how much energy needed to reheat the water to 50°C?
  
• An ideal refrigerator-freezer operates with COP = 7.0 in a 24°C room.What is the temperature inside the freezer?
  
• What volume of water at 0°C can a freezer make into ice cubes in 1.0 hour,if the coefficient of performance of the cooling unit is 7.0 and the power input is 1.0 kilowatt?
  
• When 53000000J of heat is added to a gas enclosed in a cylinder fitted with a light friction less piston maintained at atmospheric pressure,the volume is observed to increase from 1.9m^3 to 4.1 m^3.What is the change in internal energy of the gas?
  
• An athletic association wants to sponsor footrace.The average time to run the course is 58.6 min, with a s.deviation of 43 min.If the association give certificates to the fastest 20% of the racers, what should the cutoff time be? (normally distribution)