An instrument used to measure the airspeed on many early low-speed airplanes, principally during 1919 to 1930, was the venturi tube. this simple device is a convergent–divergent duct. (the front section’s cross-sectional area a decreases in the fl ow direction, and the back section’s cross-sectional area increases in the fl ow direction. somewhere between the inlet and exit of the duct, there is a minimum area called the throat .) see fi gure below. let a 1 and a 2 denote the inlet and throat areas, respectively. let p 1 and p 2 be the pressures at the inlet and throat, respectively. the venturi tube is mounted at a specifi c location on the airplane (generally on the wing or near the front of the fuselage) where the inlet velocity v 1 is essentially the same as the free-stream velocity—that is, the velocity of the airplane through the air. with a knowledge of the area ratio a 2 / a 1 (a fi xed design feature) and a measurement of the pressure difference p 1 − p 2 , we can determine the airplane’s velocity. for example, assume aa 21 a 1 4/ a a a = and p 1 − p 2 = 80 lb/ft 2 . if the airplane is fl ying at standard sea level, what is its velocity?

Aroll in a paper machine is powered by a separately excited dc machine. operating point 1 (under load): the roll typically operates at 764 rpm and must provide 301 nm of torque to oppose the load of the paper. the armature voltage is 230v for this operating point operating point 2 (no load): when the load is removed the speed of the roll increases to 900 rpm (the field characteristics are unchanged) la ea dev m (a) calculate the maximum torque (units of nm) that the motor can supply with this applied voltage (b) calculate the value of the armature resistance, ra (in ohms) (c) at operating point 1 (loaded condition), the field current, i, and the total input power (armature field), are measured to be to be 10 a and 28,600 w respectively. use this information to calculate the value of the field resistance, rf (in ohms). (d) (d) at operating point 1 (loaded condition), calculate the motor efficiency. express your answer as a percent to at least 2 significant digits. (d) if the field voltage is reduced by 1/2, calculate the new stall torque (in nm) of the motor (f). if the field voltage is reduced by 1/2, calculate the new no-load speed (in rad/sec)

Which of the following is not a characteristic of s waves? a. travel slower than p waves. b. cannot be detected in locations more than 105° from an earthquake’s epicenter. c. travel through solids and liquids. d. only affect coastal regions.

Why is it important always to use horizontal bars in unit fractions when performing unit conversions?