When you lean forwards, you shift some mass of your upper body forwards away fro
ID: 2118224 • Letter: W
Question
When you lean forwards, you shift some mass of your upper body forwards away from your hips. This creates a turning effect causing you to topple forwards. The muscles of your lower back contract and produce a torque to counteract this forwards turning effect and keep you steady. If your upper body weighs 100 pounds and by leaning forwards you shift the center of mass of your upper body forwards by 0.5 feet, what must be the size of the torque generated by the lower back muscles to counteract this weight shift (just calculate the size, not the + or - or units)?
Angular momentum is conserved, and is the product of moment of inertia and angular velocity. Which of the following statements accurately reflects the relationship between decreasing moment of inertia to increase angular velocity?
Answer
1.
A soccer player bends their knee during the backswing of their kicking motion so they can swing towards the ball with great speed.
2.
A long jumper puts their arms up in the air to control their forwards rotation in flight.
3.
A discus thrower will make their whole body position as wide as possible at the instant of release to increase their rotational speed, which they can transfer to the discus.
4.
A softball pitcher will release the ball with their arm fully extended to make sure they are throwing at the maximum possible angular velocity of their arm.
The size of a torque depends on two things: the size of the associated linear force and the moment arm. Which of the following statements best defines a moment arm?
Answer
1.
The moment arm is the straight line distance from the axis of rotation to the point of application of the linear force
2.
The moment arm is the average distance between forces acting around an axis of rotation
3.
The moment arm is the longest possible straight line distance from the axis of rotation to the point of application of the linear force
4.
The moment arm is the shortest possible straight line distance from the axis of rotation to the line of the linear force
Why do people walking, jogging, and running move their right arm with their left leg and their left arm with their right leg?
Answer
1.
Because moving your leg forwards by itself creates an undesirable rotation in the transverse plane, so moving the arm on the opposite side balances out that transverse rotation and allows you to keep traveling straight ahead
2.
Because moving your leg forwards by itself creates an undesirable rotation in the sagittal plane, so moving the arm on the opposite side balances out that sagittal rotation and allows you to keep traveling straight ahead
3.
Because moving your leg forwards by itself creates an undesirable rotation in the coronal plane, so moving the arm on the opposite side balances out that coronal rotation and allows you to keep traveling straight ahead
4.
Because moving your leg forwards by itself creates an undesirable rotation in the frontal plane, so moving the arm on the opposite side balances out that frontal rotation and allows you to keep traveling straight ahead
Why do runners flex the knees and hips of their recovery legs during the swing phase?
Answer
1.
This action increases the moment of inertia of the leg about the hip joint, which causes an increase in the rotation speed of the leg, and an increased torque requirement to move the leg, resulting in an overall increase of energy expenditure
2.
This action decreases the moment of inertia of the leg about the hip joint, which causes an increase in the rotation speed of the leg, and a decreased torque requirement to move the leg, resulting in an overall decrease of energy expenditure
3.
This action decreases the moment of inertia of the leg about the hip joint, which causes an increase in the rotation speed of the leg, but an increased torque requirement to move the leg, resulting in an overall increase of energy expenditure
4.
This action increases the moment of inertia of the leg about the hip joint, which causes a decrease in the rotation speed of the leg, and a decreased torque requirement to move the leg, resulting in an overall decrease of energy expenditure
Your muscles insert close to your joints, which allows you great freedom of movement, but demands great force production from the muscles to produce the movement. When you hold a 20 pound dumbbell in your hand and extend it away from your body, the combined weight and location of your arm and the dumbbell can create a torque of 60 foot-pounds about your shoulder. If the moment arm of your deltoid muscle is 0.2 (1/5) feet, what muscle force is needed to counteract the torque of 60 foot-pounds? (just calculate the size, not the + or - or units)?
1.
A soccer player bends their knee during the backswing of their kicking motion so they can swing towards the ball with great speed.
2.
A long jumper puts their arms up in the air to control their forwards rotation in flight.
3.
A discus thrower will make their whole body position as wide as possible at the instant of release to increase their rotational speed, which they can transfer to the discus.
4.
A softball pitcher will release the ball with their arm fully extended to make sure they are throwing at the maximum possible angular velocity of their arm.
Explanation / Answer
1)d
2)c
3)d
4)a
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