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Bruce Lee was famous for breaking concrete blocks with a single karate chop. From slow-motion video, the speed of his 1.50-kg hand descending on a block was estimated to be 15.0 m/s, which decreased to a speed of 0.500 m/s in the 2.50 × 10−3 s during which his hand made contact with and broke through the block. The maximum shear stress a concrete block can be subjected to before breaking is 9.50 × 105 N/m2. a. What was the force exerted by Lee’s hand on the block? b. If a typical concrete block broken by Lee was 3.00 cm thick and 15.2 cm wide, what is the shear stress experienced by the concrete block? c. Will the concrete block succumb to Lee’s karate chop?
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Chapter 14 Solutions
Physics for Scientists and Engineers: Foundations and Connections
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- A horizontal, rigid bar of negligible weight is fixed against a vertical wall at one end and supported by a vertical string at the other end. The bar has a length of 50.0 cm and is used to support a hanging block of weight 400.0 N from a point 30.0 cm from the wall as shown in Figure P14.81. The string is made from a material with a tensile strength of 1.2 108 N/m2. Determine the largest diameter of the string for which it would still break. FIGURE P14.81arrow_forwardA vibration sensor, used in testing a washing machine, consists of a cube of aluminum 1.50 cm on edge mounted on one end of a strip of spring steel (like a hacksaw blade) that lies in a vertical plane. The strips mass is small compared with that of the cube, but the strips length is large compared with the size of the cube. The other end of the strip is clamped to the frame of the washing machine that is not operating. A horizontal force of 1.43 N applied to the cube is required to hold it 2.75 cm away from its equilibrium position. If it is released, what is its frequency of vibration?arrow_forwardWhy is the following situation impossible? A worker in a factory pulls a cabinet across the floor using a rope as shown in Figure P12.36a. The rope make an angle = 37.0 with the floor and is tied h1 = 10.0 cm from the bottom of the cabinet. The uniform rectangular cabinet has height = 100 cm and width w = 60.0 cm, and it weighs 400 N. The cabinet slides with constant speed when a force F = 300 N is applied through the rope. The worker tires of walking backward. He fastens the rope to a point on the cabinet h2 = 65.0 cm off the floor and lays the rope over his shoulder so that he can walk forward and pull as shown in Figure P12.36b. In this way, the rope again makes an angle of = 37.0 with the horizontal and again has a tension of 300 N. Using this technique, the worker is able to slide the cabinet over a long distance on the floor without tiring. Figure P12.36 Problems 36 and 44.arrow_forward
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- the drawing shows a 150 kg crate hanging from one end of steel bar (S= 8.1 x10^10 n/m^2) The length of the bar is 0.428 m and its cross-sectional area is 7.94 x 10 ^-4 m^2. Neglect the weight of the bar itself and determine (a) the shear stress on the bar and (b) the vertical deflection deltaY of the right end of the bar.arrow_forwardSteel beams are used for load bearing supports in a building. Each beam is 4.0 m long with a cross-sectional area of 7.5 10-3 m2 and supports a load of 4.5 104 N. Young's modulus for steel is 210 ✕ 109 N/m2. a) How much compression (in mm) does each beam undergo along its length? b) Determine the maximum load (in N) one of these beams can support without any structural failure if the compressive strength of steel is 1.50 ✕ 108 N/m2.arrow_forwardIf a 6.0 x 10^3 mm elastic cable of density 1.1 x 10^3 kg/m^3 is dangling, how much does the length change due to its own weight? NOTE: Suppose its young���s modulus is Y = 1.0 x 10^6 N/m^2arrow_forward
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