The pendulum consists of a slender 6-kg rod ab and 9-kg disk. it is released from rest without rotating. when it falls 0.3 m, the end a strikes the hook s, which provides a permanent connection. determine the angular speed of the pendulum after it has rotated 90 degree. treat the pendulum's weight during impact as a non-impulsive force.

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?