A convex lens has focal length f. An object is placed at 2f on the axis. The image formed is located
A)
between 2f and infinity.
B)
at 2f.
C)
between f and 2f.
D)
at f.
B
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Benzene flowing at 12.5 kg/s is to be cooled continuously from 80°C to 54°C by 10 kg/s of water available at 15.5°C. Using Table 10.6, estimate the surface area required for (a) cross-flow with six tube passes and one shell pass with neither of the fluids mixed and (b) a counterflow exchanger with one shell pass and eight tube passes with the colder fluid inside tubes.
GIVEN
• Benzene coded by water in a heat exchanger
• Benzene flow rate m b= 12.5 kg/s
• Water flow rate m w= 10 mg/s
• Benzene temperatures
? (Tb,in) = 82°C
? (Tb,out) = 54°C
• Water inlet temperature (Tw,in) = 15.5°C
FIND
The surface area required for (a) Cross-flow, 6 tube passes, 1 shell pass, both unmixed (b) Counterflow, 8 tube passes, 1 shell pass, water in tubes
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at 20°C (cpw) = 4182 J/(kg K)
the specific heat of Benzene at 68°C (cpb) = 1926 J/(kg K)
Rotational Kinetic Energy: A string is wrapped tightly around a fixed pulley that has a moment of inertia of 0.0352 kg ? m2 and a radius of 12.5 cm. A mass of 423 g is attached to the free end of the string. With the string vertical and taut, the mass is gently released so it can descend under the influence of gravity. As the mass descends, the string unwinds and causes the pulley to rotate, but does not slip on the pulley. What is the speed of the mass after it has fallen through 1.25 m?
A. 2.00 m/s B. 2.28 m/s C. 1.97 m/s D. 3.94 m/s E. 4.95 m/s
The first of two identical boxes of mass m is sitting on level ground. The second box is sitting on a ramp that makes a 20° angle with the ground. The normal force of the level ground on the first box is 
; the normal force of the ramp on the second box is 
. Which statement is correct?
A.
= = mg.B.
= mg; = mg sin 20°.C.
= mg; = mg cos 20°.D.
= mg; = ?mg cos 20°.E.
= ? = ?mg.What is the most accurate physical analog for a particle in a box?