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10 Physics 153 Assignment 2a
Due the day of your Tutorial in the week of October 48, 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 copperbottomed 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 icewater mixture at
the other. The rod consists of 1.00m section of copper (one end in steam) joined endtoend
to a length L2 of steel (one end in ice). Both sections of the rod have crosssection areas of
4.00cm2 . The temperature of the coppersteel 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 icewater
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
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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
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10 Physics 153 Assignment 2b
Due the day of your Tutorial in the week of October 48, 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
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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.
 Spring '10
 SarahBurke,DonaldWitt,MichaelDHasinoff,AndrzejKotlicki

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