PHYS153assign2a - UB hys C ics 15 20 3 10 Physics 153...

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Unformatted text preview: UB hys C ics 15 20 3 10 Physics 153 Assignment 2a Due the day of your Tutorial in the week of October 4-8, 2010 1. (a) Two 50g ice cubes are dropped into 200g of water in a glass. If the water was initially at a temperature of 25◦ C, and if the ice came directly from the freezer at −15◦ C, what will the temperature of the drink be when the ice and water reach the same temperature? (b) How much ice is left? (c) Suppose that only one ice cube had been used in part (a), what would be the final temperature of the drink? Neglect the heat capacity of the glass. 2. A copper-bottomed saucepan containing 0.8L of boiling water boils dry in 10min. Assuming that all heat flows through the flat copper bottom, which has a diameter of 15cm and a thickness of 3.0mm, calculate the temperature of the outside of the copper bottom while some water is still in the pan. 3. A small pond has a layer of ice 1cm thick floating on its surface. (a) If the air temperature is −10◦ C, find the rate in cm per hour at which ice is added to the layer. The thermal conductivity of ice is 0.592 W/mK. (b) How long does it take for a 20cm layer to build up? 4. A long rod, insulated to prevent heat loss along its sides, is in perfect thermal contact with boiling water (at atmospheric pressure) at one end and with an ice-water mixture at the other. The rod consists of 1.00m section of copper (one end in steam) joined end-to-end to a length L2 of steel (one end in ice). Both sections of the rod have cross-section areas of 4.00cm2 . The temperature of the copper-steel junction is 65.0◦ C after a steady state has been set up. (a) How much heat per second flows from the steam bath to the ice-water mixture? (b) What is the length L2 of the steel section? 5. The hot glowing surfaces of stars emit energy in the form of electromagnetic radiation. It is a good approximation to assume star are perfect black bodies. Rigel, the bright blue star in the constellation Orion emits the brightest light at a wavelength of λ = 237.5nm and radiates energy at a rate of 2.7 × 1032 W . Find the radius of the star Rigel. 1 UB hys C ics 15 20 3 10 Problem 6. You are given a graph of temperature as a function of time for a container of ice and water mixture which is slowly heated starting at t = 0 sec. When all the ice melts, there is 850ml of water in the container. How much ice was in the container at the start, t = 0 sec? Temperature (in deg C) as a function of time 7.00 5.25 3.50 1.75 0 -1.75 0 375 750 Time in seconds 1125 1500 UB hys C ics 15 20 3 10 Physics 153 Assignment 2b Due the day of your Tutorial in the week of October 4-8, 2010 1. A freezer has accumulated 2 kg of ice and is at the temperature of −10◦ C. (a) How much heat we need to deliver to defrost it, that is melt all the ice? (b) How long it will take to defrost it with a 500 W electric heater? 2. A flow calorimeter is a device used to measure the specific heat of a liquid. Heat is added at a known rate to the liquid as it passes through the calorimeter at a known rate. Measurement of the resulting temperature difference between the inflow and outflow points of the liquid stream enables us to compute the specific heat of the liquid. Suppose a liquid of density 0.85 g/cm3 flows through the calorimeter at a rate of 8.0 cm3 /s. Heat is added at the rate of 250W by means of an electric heating coil, and a temperature difference of 15◦ C is established in steady state conditions between the outflow and inflow points. Find the specific heat of the liquid. 3. Two cylindrical rods of equal mass are made of silver and iron. If the rods are kept at the same temperature difference, then they transfer heat at the same rate. Find the ratio of the length of the two rods. ( ksilver = 420 Wm/K, ρsilver = 10.5 × 103 kg/m3 , kiron = 79 Wm/K, ρiron = 7.86 × 103 kg/m3 ) 4. At noon, the Sun delivers 1400 W/m2 of power to a blacktop road. If the road only loses energy by radiation what is its equilibrium temperature? 5. A crate of fruit with mass 35.0 kg and specific heat capacity 3650 J/kg K slides down a ramp inclined at 36.8◦ below the horizontal. The ramp is 8.00 m long. (a) If the crate was at rest at the top of the incline and has a speed of 2.50 m/s at the bottom, how much work was done on the crate by friction? (b) If an amount of heat equal to the magnitude of the work done by friction goes into the crate of fruit and the fruit reaches a uniform final temperature, what is its temperature change? 1 UB hys C ics 15 20 3 10 Problem 6. You are given a graph of temperature as a function of time for a container of ice and water mixture which is slowly heated starting at t = 0 sec. When all the ice melts, there is 850ml of water in the container. How much ice was in the container at the start, t = 0 sec? Temperature (in deg C) as a function of time 7.00 5.25 3.50 1.75 0 -1.75 0 375 750 Time in seconds 1125 1500 ...
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This note was uploaded on 11/12/2010 for the course PHYS 153 PHYS 153 taught by Professor Sarahburke,donaldwitt,michaeldhasinoff,andrzejkotlicki during the Spring '10 term at UBC.

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