Question 1

The centre of gravity (COG) is defined as:

Accepted Answer

The centre of gravity can be defined as the point at which the entire weight of an object is assumed to be concentrated.

Question 2

A person is standing upright with their arms by their sides. If they were to move their arms up over their head, their centre of gravity should:

Accepted Answer

C is correct. As a portion of the body's weight is moved upwards further from the ground, the centre of gravity should also move further upwards from the ground.

Question 3

The centre of gravity is always located within the body and cannot be located outside of the body.

Accepted Answer

The centre of gravity can be located within or outside of the body

Question 4

In a regularly-shaped object of uniform density, the centre of gravity is found at the geometric centre of the object.

Accepted Answer

In a regularly-shaped object of uniform density, the centre of gravity is found at the geometric centre of the object.

Question 5

The centre of gravity in the human body may move depending on the posture and position of the limbs.

Accepted Answer

The centre of gravity in the human body may move depending on the posture and position of the limbs, for example moving the arms from above the head down to the side of the body will result in the centre of gravity shifting downwards (towards the feet in this case)

Question 6

Stability is decreased when the centre of gravity (COG) of the object lies nearer the lower part of the object and when a vertical line through the COG falls within the base of support the object.

Accepted Answer

Stability will be increased when the centre of gravity (COG) of the object lies nearer the lower part of the object and when a vertical line through the COG falls within the base of support the object.

Question 7

State two ways the centre of gravity may influence the stability of an object

Accepted Answer

The answer of State two ways the centre of gravity...

Question 8

Use the equation 'Moment = force (Mass of limb x acceleration due to gravity) × perpendicular distance from axis of rotation' to calculate the moment about the OX axis for the hand when:
0.006 = the percentage of mass of the whole body for this segment expressed as a decimal (i.e., a proportion of 1.0 or 0.6%)
82 = athlete's mass in kilograms (kg)
9.81 = acceleration due to gravity expressed in m/s²
1.40 = perpendicular distance from OX which is 140 cm to be expressed in meters (m) along Y

Accepted Answer

The answer of Use the equation 'Moment = force (Mass...

Question 9

You have an athlete lying on a centre of gravity board. Use the formula: 
x₁ = (W₃ . d)/W₁ 
to calculate the x₁ (the horizontal distance from the fulcrum to the body centre of gravity) when: 
Athlete = 62kg
d = 3.5m
W₃ = 171N

Accepted Answer

The answer of You have an athlete lying on a...

Question 10

Which of the following statements is true regarding 'stability'

Accepted Answer

Stability can be described as the ability of an object to maintain its posture or position.

Question 11

Static equilibrium is:

Accepted Answer

Static equilibrium is when the an object or body is at rest (i.e. not moving)

Question 12

Dynamic equilibrium is:

Accepted Answer

Dynamic equilibrium is when an object or body is moving with a constant velocity (i.e. not accelerating)

Question 13

A pair of equal and opposite parallel forces that will often cause rotations of objects about specific axis is called:

Accepted Answer

A pair of equal and opposite parallel forces that will often cause rotations of objects about specific axis is called a force couple.

Question 14

If an obect is placed on a table in static equilibrium and exerts a force of - 35N onto the table, the reaction force from the table would be 35N.

Accepted Answer

If an object is in static equilibrium the sum of all forces must equal zero (0). In this case, if the object is exerting a negative (downwards) force of 35N onto the table, the table must be exerting a positive (upwards) force of 35N back onto the object.

Question 15

Resultant forces equal to two co-planar (occupying the same plane) forces acting on an object can only be solved mathematically.

Accepted Answer

Resultant forces can either be solved graphically (by actually drawing a scaled diagram and using the "tip to tail" method by joining the two forces with a third (the resultant)) or mathematically by resolving the forces and then using the first condition of equilibrium (∑F = 0) to determine the third force

Question 16

The stability of an object can be increased by lowering the center of gravity closer to the ground, increasing the base of support and maintaining the centre of gravity within the base of support. Stability is also increased in objects with greater mass.

Accepted Answer

The stability of an object can be increased by lowering the center of gravity closer to the ground, increasing the base of support and maintaining the centre of gravity within the base of support. Stability is also increased in objects with greater mass.

Question 17

An athlete is holding a 5kg dumbbell in their hand maintaining an elbow joint angle of approximately 100° of elbow flexion. Rearrange the equation "∑CWM + ∑ACWM = 0" to solve for the muscle force (F₁) needed to maintain static equilibrium, when: 
F₂ x d₂ = clockwise moment (negative) (∑CWM)
F₁ x d₁ = anti-clockwise moment (positive) (∑ACWM)
Weight force of arm, hand and dumbbell mass x acceleration due to gravity (F₂) = 9kg x 9.81m/s²
Perpendicular distance from joint axis to muscle force (d₁) = 0.04m
Perpendicular distance from joint axis to weight force (d₂) = 0.36m

Accepted Answer

The answer of An athlete is holding a 5kg dumbbell...

Question 18

Draw a free body diagram (using the tip to tail method) to measure the resultant force for the following two forces:
A force of 25N in a North-Easterly direction
A force of 15N in a North-Westerly direction

Accepted Answer

The answer of Draw a free body diagram (using the...

Question 19

What are the first and second conditions of equilibrium?

Accepted Answer

The answer of What are the first and second conditions...

Question 20

Which of the following graphs is most likely to represent the acceleration of an athlete during a 100 m sprint?

Accepted Answer

Sprinters typically lose velocity (i.e. slow down) towards the end of a 100 m sprint, thus the change in velocity and acceleration are negative. 'b' is the only option that shows a negative acceleration.

Quiz 1: Kinematics of Linear Motion

The centre of gravity (COG) is defined as:

A person is standing upright with their arms by their sides. If they were to move their arms up over their head, their centre of gravity should:

The centre of gravity is always located within the body and cannot be located outside of the body.

In a regularly-shaped object of uniform density, the centre of gravity is found at the geometric centre of the object.

The centre of gravity in the human body may move depending on the posture and position of the limbs.

Stability is decreased when the centre of gravity (COG) of the object lies nearer the lower part of the object and when a vertical line through the COG falls within the base of support the object.

State two ways the centre of gravity may influence the stability of an object

You have an athlete lying on a centre of gravity board. Use the formula: x₁ = (W₃ . d)/W₁ to calculate the x₁ (the horizontal distance from the fulcrum to the body centre of gravity) when: Athlete = 62kg d = 3.5m W₃ = 171N

Which of the following statements is true regarding 'stability'

Static equilibrium is:

Dynamic equilibrium is:

A pair of equal and opposite parallel forces that will often cause rotations of objects about specific axis is called:

If an obect is placed on a table in static equilibrium and exerts a force of - 35N onto the table, the reaction force from the table would be 35N.

Resultant forces equal to two co-planar (occupying the same plane) forces acting on an object can only be solved mathematically.

The stability of an object can be increased by lowering the center of gravity closer to the ground, increasing the base of support and maintaining the centre of gravity within the base of support. Stability is also increased in objects with greater mass.

Draw a free body diagram (using the tip to tail method) to measure the resultant force for the following two forces: A force of 25N in a North-Easterly direction A force of 15N in a North-Westerly direction

What are the first and second conditions of equilibrium?

Which of the following graphs is most likely to represent the acceleration of an athlete during a 100 m sprint?