EXERSCI 203 Biomechanics 1 SEMESTER ONE, 2023 (Exam)

发布时间：2024-06-11

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EXERSCI 203

Biomechanics 1 (Exam)

SEMESTER ONE, 2023

1 Assuming that the frame-of-reference is positive pointing upwards, explain which phase of a vertical jump has negative velocity and positive acceleration. Indicate, in this sitation, what each of (a) negative velocity and (b) positive acceleration tell us about how the movement is changing.

2 List the forces that act on a skydiver immediately after leaving an aeroplane. How do these forces, and the velocity of the skydiver change during the course of their freefall?

Briefly describe

(a) what activity is shown in the graph above, and

(b) what is happening, including the effect on the motion of the centre-of-mass, at points A and B.

4 The following figure illustrates the frontal plane hip angles and torques during a gait cycle. The joint power is calculated as the multiplication of the angular velocity and joint torque.

a. During the 0-20% of the gait cycle, will the frontal plane hip power be positive or negative? Please justify your answer.

b. During the 20-40% of the gait cycle, will the frontal plane hip power be positive or negative? Please justify your answer.

5 The figure below shows stress-strain curves for two materials labelled A and B. If 2Gpa stress is applied for both materials, which material will generate more strain? If the stress is released, will there be any energy loss? Please justify your answer.

6 A sportsperson is training by pulling a weighted sled.

When first starting out, they manage to generate a horizontal force of 750 N before the sled starts to move. If the coefficient of static friction is greater than the coefficient of kinetic friction for the sled, then describe the constant force that would be required to maintain constant power output once the sled was moving. How could the athlete change the setup to require a lower constant power level during training?

7 A resistance trainer is thinking about modifying their back squat technique. A cross-section showing their current pose at the bottom of the squat is shown below. The centre-of-mass of the torso, head, bar, and weights is shown with the symbol.

a) Recreate the red simple central skeleton of the figure in your working sheet. Indicate on your diagram the moment arm of the torso, head, bar, and weights to the knee, and also to the hip. [1 mark]

b) What effect would having a more upright posture (more vertical back) while leaving the leg positions unchanged, have on the forces required in muscles acting at the hip and knees? Justify your answer. [3 marks]

During a floor routine, a gymnast completes a somersault with a full twist. They leave the ground with no twisting motion, but start twisting in mid-air, and then land with no twisting motion.

a) Complete the following: the forward somersault can be described as a Select alternative (positive, negative) rotation around the Select alternative (anteroposterior, mediolateral, longitudinal) axis, which points Select alternative (backwards, forwards, right, down, up, left). The rotation occurs in the Select alternative (sagittal, frontal, transverse) plane.

9 (b) Briefly explain the function of 'throwing the arms' during the somersault, and how momentum can be conserved even though twisting motion starts and stops while in the air.

One risk factor for ACL injury is knee frontal plane angle (also known as varus or valgus "knock-kneed" angle) in the contact leg. A team trainer took some video footage of players performing side-steps, and measured their leg positions in the videos. One frame from this analysis is shown above. Positions of the ankle, knee, and hip in the image are shown, in units of pixels.

10 The pixel resolution of the image is 0.0014 m per pixel. What is the length of the shank segment in m?

Show all your working, including any information you think is relevant, in your working document, clearly labelled with the number of this question from the navigation bar below, and upload that to the final question in the exam.

11 What is the absolute segment angle of the shank in degrees?

。

12 Provide an expression (equation / formula) for calculating knee angle in terms of thigh and shank angle, following the standard anatomical convention for specifying joint angles.

13 What is the frontal plane knee angle in this pose, according to the standard anatomical convention?

。

A diver has jumped off their diving board. At the peak of their jump (horizontal velocity = 0 m/s), they are 20 m above the water, in the position shown above, somersaulting at 1 revolution/s with a moment of inertia of 5 kg·m2 .

14 How much time will pass before their centre-of-mass will reach the water?

15 The diver would like to achieve 2.25 more rotations before reaching the water. Will they achieve this at the current rate of rotation?

Yes

16 By how much would they need to change their moment of inertia to achieve exactly 2.25 rotations?

17 What change to body posture might achieve the desired change in moment-of-inertia?

18 While rotating at the new angular velocity, if their feet are 50 cm from the axis of rotation of the somersaults during the dive, what is the magnitude of the tangential velocity of the feet relative to the falling axis of rotation?

m/s

Just before taking off, a 60 kg diver stands stationary on the end of a diving board, with just their toes on the board. The foot movement is determined by the contact with the board, and muscles attached to their Achilles tendon, as shown in the diagram. Distances indicated on the diagram occur between these points and the ankle centre of rotation.

19 What is the vertical ground reaction force being applied to the diver's foot by the board?

20 What tension in the Achilles tendon is required to keep the foot stationary?

21 What must the compressive ankle contact force be in the vertical direction?

22 Two long bones have the same material and but different cross-sectional areas (shaded area in the picture). Which bone can sustain more torsion torque? Please justify your answer.

Select one alternative:

Hollow bone

Solid bone