A ball, of mass 100. g, is dropped from a height of 12. m. Its momentum when it strikes the ground is
A) 1.5 kg?m/s.
B) 4.8 kg?m/s.
C) 3.3 kg?m/s.
D) 2.4 kg?m/s.
E) 1.8 kg?m/s.
A
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A mercury-in-glass thermometer at 40°C (OD = 1 cm) is inserted through duct wall into a 3 m/s air stream at 66°C. This can be modelled as cylinder in cross-flow, as shown in figure. Estimate the heat transfer coefficient between the air and the thermometer.
GIVEN
• Thermometer in an air stream
• Thermometer temperature (Ts) = 40°C
• Thermometer outside diameter (D) = 1 cm = 0.01 m
• Air velocity (V) = 3 m/s
• Air temperature (Tb) = 66°C
FIND
• The heat transfer coefficient ch
ASSUMPTIONS
• Steady state
• Turbulence in the free stream approaching the thermometer is low
• Effect of the duct walls in negligible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at the bulk temperature of 66°C
Thermal conductivity (k) = 0.0282 W/(m K) Kinematic viscosity (?) = 20*10-6 m2/s Prandtl number (Pr) = 0.71 At the thermometer surface temperature of 40°C, the Prandtl number (Prs) = 0.71
The power of a lens is 4.0 diopters and its diameter is 5.0 cm. What is the focal length of this lens?
A) 25 cm B) 55 cm C) 10 cm D) 0.25 cm E) 2.5 cm
For a closed surface through which the net flux is zero, each of the following four statements could be true. Which of the statements must be true? (There may be more than one.)
(a) There are no charges inside the surface. (b) The net charge inside the surface is zero. (c) The electric field is zero everywhere on the surface. (d) The number of electric field lines entering the surface equals the number leaving the surface.
1.(a) only 2.(b) only 3.(b) and (d) 4.(a) and (d)Weight and normal force are action-reaction pairs
Indicate whether the statement is true or false