Which of the following is considered by biologists to be a likely place where life first arose on Earth?
A) on meteorites that landed on Earth
B) on land surfaces that got moderately heavy rainfall
C) in hot water near undersea volcanoes
D) deep underground
C
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An alpha particle (m = 6.7 × 10^?27 kg, q = +3.2 × 10^?19 C) has a speed of 20 km/s at point A and moves to point B where it momentarily stops. Only electric forces act on the particle during this motion. Determine the electric potential difference VA ? VB
a. +4.2 V b. ?4.2 V c. ?9.4 V d. +9.4 V e. ?8.4 V
A steel plate weighing 27 kN is hoisted by a cable sling that has a clevis at each end. The pins through the clevises are 22 mm in diameter. Each half of the cable is at an angle of 358 to the vertical. The average shear stress in each pin is approximately:
(A) 22 MPa
(B) 28 MPa
(C) 40 MPa
(D) 48 MPa
In addition to nitrogen, the other main components of Titan's atmosphere are
A) ammonia and water vapor B) hydrogen and helium C) oxygen and carbon dioxide D) hydrocarbons like methane and ethane
Water entering a shell-and-tube heat exchanger at 35°C is to be heated to 75°C by an oil. The oil enters at 110°C and leaves at 75°C. The heat exchanger is arranged for counterflow with the water making one shell pass and the oil two tube passes. If the water flow rate is 68 kg per minute and the overall heat transfer coefficient is estimated from Table 10.1 to be 320 W/(m2 K), calculate the required heat exchanger area.
GIVEN
• One shell pass, two tube passes counterflow heat exchanger with water in shell, oil in tube
• Water temperatures Tw,in = 35°C Tw,out = 75°C
• Oil temperatures To,in = 110°C Tw,out = 75°C
• Water flow rate m n= 68 kg/min = 1.133 kg/s
• Overall heat transfer coefficient (U) = 320 W/(m2 K)
FIND
• The required area (A)
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at the average temperature of 55°C (cpw)= 4180 J/(kg K)