Molecular Bonds: In general, which of the following is usually the weakest bond?
A. hydrogen bond
B. van der Waals bond
C. ionic bond
D. covalent bond
Answer: B
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To which of the following two-object systems can we apply conservation of momentum, and why? In each case, answer “A” if we can apply conservation of momentum because the system floats in space, “F” if it’s because the system is functionally isolated, “C” if it’s because the system undergoes a collision, and “D” if momentum is not conserved at all because the system is not isolated.
(a) Two magnetic hockey pucks slide on a flat plane of frictionless ice. They attract each other as they pass, changing each other’s trajectories without touching. (b) An asteroid imbeds itself in a planet. (c) An isolated star passes through a well-defined cloud of gas, and is slowed by friction in this process. (Assume that we can keep track of the cloud’s momentum.) (d) Two people dance the tango. (e) Two people riding personal hovercraft tug on each other with a rope. (f) A cannonball drops to the earth and lands with a thud, burying itself in the ground.
A nearsighted person has a far point of 33 cm. What focal length contact lens would allow her to see in the distance?
A. 33 cm B. -33 cm C. 67 cm D. -67 cm E. 3.0 m
A long cylinder of 0.1-m-diameter has a surface temperature of 400 K. If it is immersed in a fluid at 350 K, natural convection will occur as a result of the temperature difference. Calculate the Grashof and Rayleigh numbers that will determine the Nusselt number if the fluid is
(a) Nitrogen
(b) Air
(c) Water
(d) Oil
(e) Mercury
GIVEN
• A long cylinder immersed in fluid
• Diameter (D) = 0.1 m
• Surface temperature (Ts) = 400 K
• Fluid temperature (T?) = 350 K
FIND
The Grashof number (Gr) and the Rayleigh number (Ra) if the fluid is
(a) Nitrogen (b) Air (c) Water (d) Oil (e) Mercury
ASSUMPTIONS
• The cylinder is in a horizontal position (the characteristic length is the diameter of the cylinder)
SKETCH
PROPERTIES AND CONSTANTS
The thermal expansion coefficients for oil and mercury can be estimated from
Suppose you live on the Moon. How long is a day (i.e. from sunrise to sunrise)?
24 hours a lunar month 23 hours 56 minutes a year