Imagine for a minute that the Moon is held in its orbit about the Earth by electrical forces rather than by gravitation. What electrical charges ?Q on the Earth and +Q on the Moon are necessary to hold the Moon in a circular orbit with a period of 27.3 days? The Earth-Moon distance is 384,000 km and the mass of the Moon is 7.35 × 10^22 kg
Q = 5.73 × 10^13 C
You might also like to view...
An object is placed 50 cm in front of a concave mirror with a focal length of 25 cm. What is the magnification produced by the mirror?
A) -0.50 B) -1.0 C) +1.5 D) -2.0 E) +1.0
A straight wire carries a current of 40 A in a uniform magnetic field (magnitude = 80 mT). If the force per unit length on this wire is 2.0 N/m, determine the angle between the wire and the magnetic field.
A. either 39° or 141° B. either 25° or 155° C. either 70° or 110° D. either 42° or 138° E. either 65° or 115°
A ball thrown upwards reaches a maximum height and then comes back down to the original level. As the ball is going upwards, the velocity points __________ and the acceleration points __________
Fill in the blank(s) with correct word
A shell-and-tube heat exchanger is to be used to cool 25.2 kg/s of water from 38°C to 32°C. The exchanger has one shell-side pass and two tube side passes. The hot water flows through the tubes and the cooling water flows through the shell. The cooling water enters at 24°C and leaves at 32°C. The shell-side (outside) heat transfer coefficient is estimated to be 5678W/(m 2 K). Design specifications require that the pressure drop through the tubes be as close to 13.8 kPa as possible and that the tubes be 18 BWG copper tubing (1.24 mm wall thickness), and each pass is 4.9 m long. Assume that the pressure losses at the inlet and outlet are equal to one and one half of a velocity heat (?V2/gc), respectively. For these specifications, what tube diameter and how many tubes are needed?
GIVEN
A water-to-water shell-and-tube exchanger, hot water in tubes, cooling water in shell One shell and two tube passes Hot water flow rate m
h= 25.2 kg/s Water temperatures
? Hot: Th,in = 38°C Th,out = 32°C
? Cold: Tc,in = 24°C Tc,out = 32°C Shell-side transfer coefficient h o= 5678 W/(m2 K) Pressure drop (?p) = 13.8 kPa Tube wall thickness (t) = 1.24 mm = 0.00124 m Tube length per pass (Lp) = 4.9 m
FIND
The tube diameter (Do) and number of tubes (N)
ASSUMPTIONS
Pressure losses at inlet and outlet (?pii) = 1.5 (? V2/gc) Variation of thermal properties with temperature is negligible Fouling resistance is negligible Thermal resistance of the tube walls is negligible
SKETCH
PROPERTIES AND CONSTANTS
for water at 30°C Density (?) = 995.7 kg/m3
Specific heat (cp) = 4176 J/(kg K)
Thermal conductivity (k) = 0.615 W/(m K)
Kinematic viscosity (?) = 0.805 × 10–6 m2/s
Prandtl number (Pr) = 5.4