Deck 13: The Conditions of Rotary Motion

Question 1

Based on the principles of levers, which of the following levers is most efficient in overcoming a resistance of 20 lbs?

A) EA = 2", RA = 4"
B) EA = 4", RA = 6"
C) EA = 10", RA = 5"
D) EA = 10", RA = 10"

Answer 1

EA = 10", RA = 5"

Question 2

Where would moment of inertia be found?

A) only in sports objects
B) in objects undergoing angular motion
C) in objects undergoing linear motion
D) only in humans

Answer 2

in objects undergoing angular motion

Question 3

Why is a second-class lever well adapted to moving heavy loads?

A) axis is located between effort and resistance
B) effort is located between axis and resistance
C) effort arm is longer than resistance arm
D) resistance arm is longer than effort arm

Answer 3

effort arm is longer than resistance arm

Question 4

Calculate F for equilibrium.

A) 45 lbs.
B) 57.5 lbs.
C) 75 lbs.
D) none of the above

Question 5

In circular motion what characterizes centripetal force?

A) outward seeking force
B) moment of force
C) pulling toward the center
D) mass times displacement

Question 6

What does a machine with a resistance arm greater than a force arm favor?

A) speed
B) force
C) acceleration
D) torque

Question 7

Which of the following actions increase torque?
1) apply greater force
2) apply force at an angle closer to 90 ^$\circ$
3) lengthen perpendicular distance between axis and point of application of force
4) shorten the force arm

A) apply greater force AND shorten the force arm
B) apply greater force AND apply force at an angle closer to 90 ^$\circ$
C) apply force at an angle closer to 90 ^$\circ$ AND lengthen perpendicular distance between axis and point of application of force AND shorten the force arm
D) apply greater force AND apply force at an angle closer to 90 ^$\circ$ AND lengthen perpendicular distance between axis and point of application of force

Question 8

Why would a coach recommend a "tighter" tuck to enable a gymnast to get all the way around?

A) angular velocity will decrease
B) angular displacement will decrease
C) moment of inertia will decrease
D) mass will decrease

Question 9

In which of the following will the least amount of force be necessary to overcome a 20 lb. resistance?

A) angle of pull = 30 ^$\circ$ , effort arm = 3"
B) angle of pull = 45 ^$\circ$ , effort arm = 2"
C) angle of pull = 60 ^$\circ$ , effort arm = 4"
D) angle of pull = 120 ^$\circ$ , effort arm = 1"

Question 10

What is the true effort arm (moment arm) of a lever in the body?

A) distance from axis to point of attachment of muscle
B) distance from midpoint of muscle's line of pull to axis
C) perpendicular distance from axis to point of application of force
D) perpendicular distance from line of pull of muscle to axis

Question 11

A machine that magnifies force does so at the expense of:

A) velocity and speed
B) velocity and acceleration
C) displacement and torque
D) speed and range of motion

Question 12

In which of the following is torque not found?

A) seesaws
B) bowling ball rolling down alley
C) linear motion
D) animals

Question 13

Why is it more difficult to perform a sit-up when the hands are clasped behind the head then when the arms are kept at the side?

A) the resistance arm is greater
B) the resistance arm is smaller
C) the torque of the resistance is reduced
D) the torque produced by the abdominals is reduced

Question 14

Why lift a heavy weight from the floor by flexing and then extending the knees rather than flexing at the hips and then lifting the trunk?

A) longer lever
B) less force available
C) shorter resistance arm
D) smaller angle of pull

Question 15

What is the effort (E) and what is the resistance (R) acting on the femur during flexion of the knee of the supporting leg when going down a step?

A) E = concentric contraction of the hamstring, R = weight
B) E = concentric contraction of the vasti, R = weight
C) E = weight, R = eccentric contraction of the hamstrings
D) E = weight, R = eccentric contraction of the vasti

Question 16

Why is it easier for a runner to move his recovery leg forward more rapidly when it is flexed than when extended?

A) mass of the leg is greater when it is flexed
B) mass of the leg is less when it is flexed
C) moment of inertia of the leg is greater when leg is flexed
D) moment of inertia of the leg is less when leg is flexed

Question 17

A ten-pound weight is held so that it can be moved in either direction by the biceps and triceps (e.g. arm abducted with flexion and extension in the horizontal plane). How much effort will the triceps need as compared to the biceps where the effort arm is 1 inch for the triceps and 2 inches for the biceps? The weight is held in the hand at a point 12 inches from the elbow.

A) triceps 2 1/2 times as much as biceps
B) triceps 2 times as much as biceps
C) triceps same as biceps
D) triceps 1/2 as much as biceps

Question 18

Which of the following joint actions represents a third class lever?

A) ankle joint in the push-off of a jump
B) elbow joint in shot put
C) hip joint in lifting leg when stepping up on a bench
D) humeral joint in controlled adduction from an abducted position

Question 19

What is centrifugal force?

A) force that causes object to fly off at a tangent to arc of motion
B) force that causes object to travel in an arc
C) reaction force to that which pulls away from center of arc
D) reaction force to centripetal force
Short Answer Questions

Question 20

What is meant by torque?

A) ability of a force to overcome resistance
B) amount of force necessary to cause rotation
C) effective force producing rotary motion at an axis
D) relationship between force and resistance

Question 21

When doing an iron cross on the still rings the ideal position is for the gymnast to support the body with the arms abducted to 90 ^$\circ$ . Why do many gymnasts abduct only to 70 ^$\circ$ on this move?

Question 22

Why can one loosen a bolt with a long handled wrench when the same bolt is impossible to move with a short handled wrench?

Question 23

Why is it easier for a gymnast doing giant swings to stop in a handstand at the top of the bar than to stop in a long hang at the bottom of the bar?

Question 24

Why do sprinters lean when running the curve on a track?

Question 25

Will a subject who is seated be able to support more weight with the knee fully extended or with the knee at 20 ^$\circ$ of flexion (lower leg 20 ^$\circ$ below the horizontal)?
Explain your answer, including a discussion of both the resistance and the effort.