Thermal Storage Solar heating of a house is much more efficient if there is a way to store the thermal energy collected during the day to warm the house at night. Suppose one solar-heated home utilizes a concrete slab of area 12 m 2 and 25 cm thick. (a) If the density of concrete is 2400kg/m 3 , what is the mass of the slab? (b) The slab is exposed to sunlight and absorbs energy at a rate of 1.4 × 10 7 J/h for 10 h. If it begins the day at 22 °C and has a specific heat of 750J/(kg.K), what is its temperature at sunset? (c) Model the concrete slab as being surrounded on both sides (contact area 24 m 2 ) with a 2.0-m-thick layer of air in contact with a surface that is 5.0 °C cooler than the concrete. At sunset, what is the rate at which the concrete loses thermal energy by conduction through the air layer? (d) Model the concrete slab as having a surface area of 24 m 2 and surrounded by an environment 5.0 °C cooler than the concrete. If its emissivity is 0.94, what is the rate at which the concrete loses thermal energy by radiation at sunset?
Thermal Storage Solar heating of a house is much more efficient if there is a way to store the thermal energy collected during the day to warm the house at night. Suppose one solar-heated home utilizes a concrete slab of area 12 m 2 and 25 cm thick. (a) If the density of concrete is 2400kg/m 3 , what is the mass of the slab? (b) The slab is exposed to sunlight and absorbs energy at a rate of 1.4 × 10 7 J/h for 10 h. If it begins the day at 22 °C and has a specific heat of 750J/(kg.K), what is its temperature at sunset? (c) Model the concrete slab as being surrounded on both sides (contact area 24 m 2 ) with a 2.0-m-thick layer of air in contact with a surface that is 5.0 °C cooler than the concrete. At sunset, what is the rate at which the concrete loses thermal energy by conduction through the air layer? (d) Model the concrete slab as having a surface area of 24 m 2 and surrounded by an environment 5.0 °C cooler than the concrete. If its emissivity is 0.94, what is the rate at which the concrete loses thermal energy by radiation at sunset?
Thermal Storage Solar heating of a house is much more efficient if there is a way to store the thermal energy collected during the day to warm the house at night. Suppose one solar-heated home utilizes a concrete slab of area 12 m2 and 25 cm thick. (a) If the density of concrete is 2400kg/m3, what is the mass of the slab? (b) The slab is exposed to sunlight and absorbs energy at a rate of 1.4 × 107 J/h for 10 h. If it begins the day at 22 °C and has a specific heat of 750J/(kg.K), what is its temperature at sunset? (c) Model the concrete slab as being surrounded on both sides (contact area 24 m2) with a 2.0-m-thick layer of air in contact with a surface that is 5.0 °C cooler than the concrete. At sunset, what is the rate at which the concrete loses thermal energy by conduction through the air layer? (d) Model the concrete slab as having a surface area of 24 m2 and surrounded by an environment 5.0 °C cooler than the concrete. If its emissivity is 0.94, what is the rate at which the concrete loses thermal energy by radiation at sunset?
A pendulum has a 0.4-m-long cord and is given a tangential velocity of 0.2 m/s toward the
vertical from a position 0 = 0.3 rad.
Part A
Determine the equation which describes the angular motion.
Express your answer in terms of the variable t. Express coefficients in radians to three significant figures.
ΜΕ ΑΣΦ
vec
(t)=0.3 cos (4.95t) + 0.101 sin (4.95t)
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Part A
■Review
The uniform 150-lb stone (rectangular block) is being turned over on its side by pulling the
vertical cable slowly upward until the stone begins to tip.
(Figure 1)
If it then falls freely (T = 0) from an essentially balanced at-rest position, determine the speed at which the corner A strikes the pad at B. The stone does not slip at its corner C as it falls. Suppose that height of the stone is
L = 1.2 ft.
Express your answer to three significant figures and include the appropriate units.
?
ft
VA 10.76
S
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Consider the circuit shown in the figure. The battery has emf ε = 69 volts and negligible internal resistance. The inductance is L = 0.4 H and the resistances are R 1 = 12 Ω and R 2 = 9.0 Ω. Initially the switch S is open and no currents flow. Then the switch is closed. After leaving the switch closed for a very long time, it is opened again. Just after it is opened, what is the current in R 1?
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