A machinist turns the power on to a grinding wheel, which is at rest at time t = 0.00 s. The wheel accelerates uniformly for 10 s and reaches the operating angular velocity of
The wheel is run at that angular velocity for 37 s and then power is shut off. The wheel decelerates uniformly at until the wheel stops. In this situation, the time interval of angular deceleration (slowing down) is closest to:
A) 17 s
B) 15 s
C) 19 s
D) 21 s
E) 23 s
Answer: A
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Refer to the figure above showing the abundance of elements in the galaxy relative to hydrogen. What is the general trend in elemental abundance?
A) Elements with more protons are less abundant. B) Elements with more protons are more abundant. C) Elements heavier than iron do not exist. D) Elements heavier than iron are relatively abundant. E) There is no apparent trend in the abundance of elements.
Currently in the USA, SETI programs are mostly funded
A) privately B) by the US Government C) by the United Nations D) by the National Academy of Sciences
A stone is held at a height h above the ground. A second stone with four times the mass of the first one is held at the same height. The gravitational potential energy of the second stone compared to that of the first stone is
A) one-fourth as much. B) one-half as much. C) twice as much. D) four times as much. E) the same.
Water at 20°C enters a 1.91-cm-ID, 57-cm-long tube at a flow rate of 3 gm/s. The tube wall is maintained at 30°C. Determine the water outlet temperature. What error in the water temperature results if natural convection effects are neglected?
GIVEN
• Water flowing through a tube
• Entering water temperature (Tb,in) = 20°C
• Tube inside diameter (D) = 1.91 cm = 0.0191 m
• Tube length (L) = 57 cm = 0.57 m
• Mass flow rate (m) = 3 gm/s = 0.003 kg/s
• Tube wall surface temperature (Ts) = 30°C
FIND
(a) The water outlet temperature (Tb,out)
(b) Percent error in water temperature rise if natural convection is neglected
ASSUMPTIONS
• Steady state
• Tube temperature is uniform and constant
• The tube is horizontal
SKETCH
PROPERTIES AND CONSTANTS
for water at 20°C
Specific heat (c) = 4182 J/(kg K)
Thermal conductivity (k) = 0.597 W/(m K)
Kinematic viscosity (?) = 1.006 × 10–6 m2/s
Prandtl number (Pr) = 7.0
Absolute viscosity (?b) = 993 × 10–6 (Ns)/m2
Thermal expansion coefficient (?) = 2.1 × 10–4 1/K At 30°C ?s = 792 × 10–6 (Ns)/m2