A sphere is constructed of two concentric parts. The inner part is a solid sphere of radius 10.0 cm made of a material with density 4000 kg/m3. The outer part is a spherical shell with inner radius 10.0 cm and outer radius 20.0 cm
The material in the outer shell has a density 9000 kg/m3.
(a) What is the mass of the sphere?
(b) What is the average density of this sphere?
(a) 281 kg (b) 8.38 × 103 kg/m3
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A car traveling at a velocity v can stop in a minimum distance d. What would be the car's minimum stopping distance if it were traveling at a velocity of 2v?
(a) d. (b) square root of 2d (c) 2d. (d) 4d. (e) 8d.
On a cold winter day, the outside wall of a home is exposed to air temperature of –2°C when the inside temperature of room is at 22°C. As a result of this temperature gradient, there is heat loss through the wall to the outside. Consider the convective heat transfer coefficients for the air inside the room and at the outside wall surface to be respectively 12.0 and 28.0 W/(m2 K). If the composite room wall is modelled as a plane wall with thermal resistance per unit area of 0.5 m2 K/W, determine the temperature at the outer surface of the wall as well as the rate of heat flow through the wall per unit area. If the homeowner were to consider using a fiberglass insulation on the inside wall surface for reducing this heat loss by 50 %, what is the required thickness of this layer and the
outside wall temperature for this case?
GIVEN
• Heat transfer through a plane wall
• Air temperature
? Inside wall (Ti) = 22°C
? outside wall (To) = –2°C
• Heat transfer coefficient
? Inside wall ( ci h ) = 12 W/(m2 K)
? Outside wall ( co h ) = 28 W/(m2 K)
• Thermal resistance of a unit area (A Rw) = 0.5 (m2 K)/W FIND (a) Temperature of the outer surface of the wall (Two) (b) Rate of heat flow through the wall per unit area (q/A) (c) Thickness of fiberglass insulation inside wall surface (d) Outside wall temperature with fiberglass insulation
ASSUMPTIONS
• One dimensional heat flow
• Steady state has been reached
PROPERTIES AND CONSTANTS
Thermal conductivity
Fiber glass (k) =0.035 W/m K
SKETCH
Energy and Momentum: In a certain nuclear reactor, neutrons suddenly collide with carbon nuclei, which have 12 times the mass of neutrons. In a head-on elastic collision with a stationary carbon nucleus, what fraction of its initial speed does the neutron have after the collision?
A. 11/12 B. 1/12 C. 11/13 D. 5/6 E. 10/13
The condensation theory is an example of:
A) a catastrophic theory. B) a hot Jupiter theory. C) a collision hypothesis. D) an evolutionary theory. E) a capture theory.