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WorkShop Main Topic: Force Systems Made by: Rodrigo López Elaboration date: August 2022 1. OUTCOMES Relacionar los principios físicos mecánicos (equilibrio, leyes del movimiento) con la práctica de la actividad física y deportiva 2. ACTIVITIES Solve the following problems 2.1 Consider four forces F1, F2, F3, and F4 shown in Fig. 1. Assume that these forces are applied on an object in the xy-plane. The first, second, and third forces have a magnitude of F1 = 32 N, F2 = 45 N, and F3 = 50 N, respectively, and they make angles α = 35˚, β = 32˚, and γ = 50˚ with the positive x axis. The force F4 has a magnitude F4 = 55 N and its line of action makes an angle θ = 65˚ with the negative x axis. Figure 1 (a) Calculate the scalar components of the resultant force vector FR. (b) Calculate the magnitude FR of the resultant force. (c) Calculate an angle that the resultant force vector FR makes with the horizontal. 2.2 Emma is working in a shoe test lab measuring the coefficient of friction for tennis shoes on a variety of surfaces. The shoes are pushed against the surface with a force of 400 N, and a sample of the surface material is then pulled out from under the shoe by a machine. The machine pulls with a force of 300 N before the material begins to slide. When the material is sliding, the machine has to pull with a force of only 200 N to keep the material moving. Figure 2. a. What is the coefficient of static friction between the shoe and the material? b. What is the coefficient of dynamic friction between the shoe and the material? 2.3 A sprinter is just coming out of the starting block, and only one foot is touching the block. The sprinter pushes back (horizontally) against the block with a force of 800 N and pushes down (vertically) against the block with a force of 1000 N. Figure 3. a. How large is the resultant of these forces? b. What is the direction of the resultant force? 2.4 The ground reaction force acting on Carter during his long jump is 4500 N acting forward and upward at an angle of 78° from horizontal. Carter’s mass is 70 kg. Other than gravity, this is the only external force acting on Carter. Figure 4. a. What is the vertical component of this ground reaction force? b. What is the horizontal component of this ground reaction force? c. How big is the net force, the sum of all the external forces, acting on Carter? 2.5 The quadriceps pulls on the patella with a force of 1000 N while the patellar tendon pulls on the patella with a force of 1000 N also. The knee is in a flexed position, so the angle between these two forces is 120°. A compressive force from the femoral condyles is the only other significant force acting on the patella. If the patella is in static equilibrium, how large is the compressive force exerted by the femoral condyles on the patella? Figure 6. 2.6 How much compression acts on the hip during two-legged standing, given that the joint supports (Wt) 250 N of body weight and the abductor muscles are producing 600 N of tension Fm? Hint: use vector sum graphical method. Figure 7 2.7 The devide is sed for surgical replacement of the knee joint. If the force acting along the leg is 360 N, determine its components along the x, y and x’ and y’. Figure 8. 3. PREVIOUS KNOWLEDGE Vectorial mechanics, trigonometry and basics mathematics 4. DELIVERY DATE Look the respective platform activity 5. ADDITIONAL INFORMATION NO 6. BIBLIOGRAPHY Basic: − B1: Biomechanics of Sport and Exercise Third Edition by Peter M. McGinnis, Peter McGinnis. − B2: Biomechanics 8th Edition by Susan Hall. − B3: Basic Biomechanics of the Musculoskeletal System by M Nordin and V Frankel, Jan 20, 2012
