Introductoin to Biomechanics Exam 2 WS18

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Mryoyo15
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Introductoin to Biomechanics Exam 2 WS18

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  1. Explain what is meant by inverse dynamics. Using the xample problem of a running athlete. What are the inputs required to enable the solution of this inverse dynamics problem and what are the outputs? (3 Points)
  2. Why is it that the joint reaction forces are usually lower than the actual joint contact? (1.p)
  3. A strain gauge rosette can be used to measure the strain on a selected location of a bone surfcae. How many strain gauges are required to determine the surface strain stte of a location of interest on a bone surface and how would these gauges be arranged within the rosetter (2p)
  4. Give a reason why the cardiovascular system consists of two circuits - or in other words: Why would it be problematic if the heart was pumping blood into only one common circuit? (1p)
  5. What is meant by diastolic pressure and systolic pressure? Briefly describe how to measure these pressures using a pressure cuff (sphygmomanometer) and a stethoscope? (3p)
  6. A reservroir has to be filled with 0.8 liters of different fluids. the fluid is pumped through a 100 cm long tube of radius 3 cm. Over the entire length of the tube a pressure drop of 1 Pa is measured in case of all fluids
    a. First, the reservoir is filled with a Newtonian Fluid with viscosity = 4cP. How long does it take to fill the reservoir? (1pt) [P] = 0.1 Pa * s
    b. Second, the reservoir is filled with blood. Blood usually has yield stress 0.05 dyn/cm^2 and viscosity 3.5cP. Blood is pumped using the same tubes, while also the pressure drop is the same. How long does it take to fill the reservoir with blood? (4pt)
    [dyn] = 10^-5 N
    HINT: F = 1 - 16/7 sqrt(E) + (4/3)E - (1/21)E^4
  7. The diaphysis of a femoral bone is embedded and fixated to be tested in a material-testing-machine. Let us assume the bone to be a perfect cylinder. The length l of the bone is 98mm, outer diameter d_o 47mm and the inner diameter d_i is 21mm.
    a. If the force F, generated by the material-testing-machine is 100kN, how high is the stress at the transition from femur to embedding? (1pt)
    b. If the femur is not perfectly aligned, the central axis of the femur is tilted by an angle alpha, so that a bending moment arises. Calculate if the bone will break at a maximum angle alpha_max of 10° due to the combined stress state arsising from compression and bending.
    To simplify the model we assume that the force-vector is tilting and not the bone. The Youngs Modulus of the femur is 17Gpa while the ultimate strain is at 1.5% (4pt)

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Mryoyo15
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Re: Introductoin to Biomechanics Exam 2 WS18

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