Biomechanics 2 Exam
Sasha Cohen does a triple toe loop and rotates three times around in 1 s. What is her average angular speed during this jump?
3 rev/s
During a drive by golfer Ai Miyazato, the angular velocity of her club is zero at the top of the backswing and 30 rad/s at the bottom of the downswing just before impact with the ball. If the downswing lasts 0.30 s, what is the average angular acceleration of the club during the downswing?
100 rad/s^2
What is the average angular velocity of an object moving through 30° in 2 s?
15 degrees per second
Calculate the moment of inertia when an object's mass is 12 kg and the mass is distributed 4 m from the axis of rotation.
192 kg*m^2
What is the net torque when you are holding a 10 lb weight 1 ft from your elbow (producing a clockwise torque) and your biceps is generating a 50 lb force with a moment arm of 3 in. (producing a counterclockwise torque)?
2.5 ft per lb
A discus thrower exerts a torque of 5 Nm on a 2 kg discus. The discus has a radius of gyration of 10 cm. If this is the only torque exerted on the discus, what is its angular acceleration?
250 rad/s^2
Mike runs in lane one around a curve, while Maurice runs in lane eight around a curve. The radius of lane eight is twice as big as the radius of lane one. If Mike has to run 50 m to get fully around the curve in lane one, how far does Maurice have to run to get fully around the curve in lane eight?
Maurice is going to cover twice as much distance as Mike
Calculate the magnitude of the angular momentum if an object's moment of inertia is 50 kg·m2 and its velocity is 10 m/s.
Need more info (angular velocity)
The statement "a rotating body will maintain a state of constant angular motion unless acted on by an external torque" refers to
Newton's First Law
The SI units for torque are
Nm
On a rigid segment that is undergoing angular motion, which of the following statements is true?
The angular displacement of the two points on the segment would be equal
When a human body is airborne (e.g., when a person leaps through the air),
The body's center of gravity follows a parabolic flight, movement of arms and legs will not influence center of gravity, air resistance influences flight path of center of gravity only if it is moving rapidly
What is the relationship between torque and angular acceleration?
The greater the torque acting on the axis of rotation, the greater the acceleration of the moving body
An eccentric force
does not pass through the axis of rotation
Pronation of the ankle (subtalar joint) combines the motions of
eversion, abduction, dorsiflexion
When knee flexion is increased (heel brought to buttocks) during running, the moment of inertia of the lower extremity about the hip
is decreased
As a joint is moved through its range of motion when strength training with free weights, such as doing the arm curl, the moment arm for the muscle crossing the joint will get
longer or shorter
As a joint is moved through its range of motion when strength training with free weights, such as doing the arm curl, the moment arm for the resistance weight will get
longer or shorter
In the average female, the center of gravity is located
lower than the average male
For most segments of the human body, the segmental center of gravity is located
more proximally
Stability may be increased by
none of the above
A centric force
passes through the axis of rotation
Which of the following motions occurs primarily in the transverse (horizontal) plane?
pirouette
In the equation for moment of inertia, which variable is most influential?
radius of gyration
When shaking the head "yes," the head movement occurs in which of the following planes?
sagittal
A person riding a bicycle forward in a straight line would be moving in the
sagittal plane
You are sparring in a tae kwon do class. Your opponent executes a roundhouse kick. The average angular velocity of his kicking leg and foot is 20 rad/s. The angular displacement from his foot to your head is 5 rad. How much time do you have to move if you want to avoid being kicked in the head?
t=.25 sec
Torque is defined as
tendency of a force to cause rotation, the turning effect of a force, and product of force and moment arm
Which of the following statements is false?
the knee is proximal to the hip joint
The moment arm is defined as
the perpendicular distance from the line of action of a force to a specified axis of rotation
Angular impulse is the product of
torque and the time that torque is applied
When cycling forward in a straight line, the knee is rotating about a(n) ____ axis.
transverse
Which plane is perpendicular to the longitudinal axis?
transverse
An example of a rotation about the longitudinal axis is a
twist
Movement of the hand at the wrist toward the ulnar side of the arm is
ulnar deviation
Which of the following limb movements dominate during jumping jacks?
adduction and abduction
What is the torque if a 50 N force is applied 2 m from the axis of rotation?
100 Nm
During a golf drive, the angular velocity of the driver is 20 rad/s just before impact with the golf ball. If the distance from the club head to the axis of rotation is 2.0 m, what is the linear velocity of the club head?
40 m/s
If the moment arm is 5 cm, and the force is 100 N, the magnitude of the torque will be
5 Nm
During a trampoline routine, a gymnast is tumbling in the air at 20 rad/s in a tuck position. He then extends into a layout position and doubles his radius of gyration just before landing on the trampoline bed. How fast is his angular velocity at this instant, just before landing on the trampoline bed?
5 rad/s
For any given muscle, the moment arm is largest when the angle of muscle pull on the bone is closest to
90 degrees
The moment arm of the biceps brachii muscle about the elbow joint is largest when the angle at the elbow joint is approximately
90 degrees
For a body to be in static equilibrium
All forces and torques on the body must add up to zero, the body must be stationary
An angle formed between a body segment and a horizontal reference line is an example of
absolute angle
Which of the following motions occurs primarily in the frontal plane?
Cartwheel
What happens to your center of gravity when you add a 200 N suitcase to your hand held out to your side?
Center of gravity shifts in direction of suitcase
As an object's mass increases, what happens to its moment of inertia?
Depends on how the added mass is distributed
A gymnast dismounts the uneven parallel bars with some angular momentum about her transverse axis. Just after release, she is in a piked position. She then extends into a layout position before she lands. What happens as a result of this action?
Her moment of inertia decreases and she rotates slower
When a body is completely motionless, it is considered to be
In static equilibrium
A diver is attempting a 2 1/2 front dive in a layout position. If the dive is successful, he will rotate 2 1/2 revolutions around his transverse (somersault) axis from takeoff until water entry. The diver's average angular speed during the dive is 5 rev/s, and he is in the air for 0.40 s from takeoff to water entry. Is the dive successful?
No, she will only make 2 revs
For an object to be in static equilibrium,
Sum of forces and torques acting on object must be equal to zero
A weightlifter is attempting a biceps curl with a 200 N barbell. The moment arm of the barbell about the elbow joint is 40 cm. What torque is created by the barbell about the elbow joint?
T=80 N*m
To determine the length of a moment arm, you would measure
The perpendicular distance from the axis of rotation to the force's line of action.
A diver attempts a 1 1/2 front flip in a tuck position off the 1 m board, but only rotates 1 1/4 times (ouch!). Which of the following suggestions is NOT appropriate for the diver?
Tuck looser
A force not directed through the center of an object (an eccentric force) tends to cause
angular and linear acceleration
Which quantity causes a change in angular momentum?
angular impulse
In anatomical terminology, the front portion of the body is called
anterior
The angular distance covered by a rotating object will always be
at least equal to, or greater than the angular displacement covered by the object
The center of gravity of an object of uniform density is located
at the exact center of the object
For a rotating object, the acceleration directed toward the center of rotation is called
centripetal acceleration
The center-directed acceleration of a spinning object (e.g., a ball on a string) is called
centripetal acceleration
