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Continuation of Problem 8. Now assume that Eq. 6-14 gives the magnitude of the air drag force on the typical 20 kg stone, which presents to the wind a vertical cross-sectional area of 0.040 m2 and has a drag coefficient C of 0.80. Take the air density to be 1.21 kg/m3, and the coefficient of kinetic friction to be 0.80. (a) In kilometers per hour, what wind speed V along the ground is needed to maintain the stone’s motion once it has started moving? Because winds along the ground are retarded by the ground, the wind speeds reported for storms are often measured at a height of 10 m. Assume wind speeds are 2.00 times those along the ground. (b) For your answer to (a), what wind speed would be reported for the storm? (c) Is that value reasonable for a high-speed wind in a storm? (Story continues with Problem 65.)
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- The force of wind blowing on a window positioned at a right angle to the direction of the wind varies jointly as the area of the window and the square of the wind's speed. It is known that a wind of 30 miles per hour blowing on a window measuring 4 feet by 5 feet exerts a force of 150 pounds. During a storm with winds of 60 miles per hour, should hurricane shutters be placed on a window that measures 3 feet by 4 feet and is capable of withstanding 300 pounds of force?arrow_forwardAt an accident scene on a level road, investigators measure a car’s skid mark to be 112 m long. It was a rainy day and the coefficient of friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes.arrow_forwardA rectangular block has a length that is six times its width and a height that is three times its width. The block's surfaces are all identical except for size. When the block is placed on a horizontal tabletop so that the area in contact with the table is length ✕ width, it is found that a horizontal force of 11.6 N applied to the block is just sufficient to overcome the static friction force and cause the block to move. The block is then knocked over so that the area in contact with the table is length ✕ height. Now, what minimum horizontal force will cause the block to move?arrow_forward
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