A 1.5-mm diameter steel ball bearing (7830 kg/m3) is dropped into a tank at SAE
ID: 1818879 • Letter: A
Question
A 1.5-mm diameter steel ball bearing (7830 kg/m3) is dropped into a tank at SAE 30 oil. What is its terminal velocity? (b) If the ball bearing is instead dropped into a different oil of the same density but develops a terminal speed of 1 cm/s, what is the oil's viscosity? A 175-lb skydiver reaches a terminal velocity of 150 mph during free fall. If the frontal area of the diver is 8ft2, what are (a) the magnitude of the drag force acting on the skydiver and (b) the drag coefficient? A 14-mm-diameter sphere is dropped into a break of SAE oil. Over a portion of its downward motion, the sphere is measured to fall at 2 m/s. In the units of newtons. What is the drag force acting on the test sphere?Explanation / Answer
At terminal velocity, the diver moves with constant velocity. So, the drag force equals the gravitational force.
Drag force = mg = 150lb*32.17 ft/s^2 = 4825.5 lb ft/s^2
Velocity = 150 mph = 220 ft/s
Drag coefficient = 2F/Av^2
2*4825.5/0.7488*8*220^2 = 0.3329
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