Question 1

If an 80 kg person whose centre of mass was located 1.1 m above the ground was to maintain a rigid posture and fall forward at an angular velocity of 3.9 rad/s, calculate the moment of inertia.

Accepted Answer

The answer of If an 80 kg person whose centre...

Question 2

Calculate the linear velocity for a rigid object that is falling forward at an angular velocity of 3.5 rad/s. Assume that the centre of mass of the object is situated at a height of 0.70 m above the ground.

Accepted Answer

The answer of Calculate the linear velocity for a rigid...

Question 3

Which of the following type of loading causes a material to shorten?

Accepted Answer

Only compression causes the material to shorten.

Question 4

Which of the following type of loading causes a material to shorten on one side and lengthen on the other?

Accepted Answer

Only bending causes the material to shorten on one side and lengthen on the other.

Question 5

What is the stress experienced by a bone that has a tension load of 12kN applied to it over a cross-sectional area of 4 cm²?

Accepted Answer

12 kN = 12,000 N. There are 100 × 100 (i.e. 10,000) cm² in a m², so 4 cm² = 4/10,000 = 0.0004 m². Stress (in Pa) = Force (in N)/CSA (in m²).

Question 6

What is the strain experienced if a 0.5 m bone is shortened to 0.498 m during compression loading?

Accepted Answer

Strain = change in length/original length, and then × 100 to give the value as a percentage.

Question 7

What is 3,000,000 Pa expressed in Mega (M) Pa?

Accepted Answer

Mega represents 1 million. Thus, divide by 1,000,000 to find the answer.

Question 8

Which of the Laws of Physics is the elastic region of a stress vs strain curve an example of?

Accepted Answer

The others are all legitimate laws, but are not related to stress - strain curves.

Question 9

What units would the Modulus of Elasticity be measured in?

Accepted Answer

Modulus of Elasticity is the ratio of stiffness (N/m² or Pa) to strain (dimensionless).

Question 10

A bone sample (depth = 8 mm, width = 12 mm, length = 15 mm) failed at 335 N during tensile loading. What are the cross sectional area (CSA) and the ultimate stress for the sample. Note: use the SI units, stated in the table.

Accepted Answer

CSA is calculated by multiplying depth by width, after converting mm to m (i.e. dividing by 1000). Stress (in Pa) = Force (in N)/CSA (in m²), and then converted by MPa by dividing by 1,000,000.

Question 11

Stress is measured in N·m^-2 and strain is dimensionless

Accepted Answer

N·m^-2 is the same as N/m², and one N·m^-2 or N/m² is equal to one Pascal (Pa).

Question 12

Stress is measured in N/m² and strain is represented as a proportion

Accepted Answer

N·m^-2 is the same as N/m², and one N·m^-2 or N/m² is equal to one Pascal (Pa).

Question 13

Stress is measured in Pa and strain is represented as a percentage

Accepted Answer

N·m^-2 is the same as N/m², and one N·m^-2 or N/m² is equal to one Pascal (Pa).

Question 14

If a collection of balls were dropped from the same height onto the same concrete surface, which of the following coefficient of restitution values would most likely correspond to the interaction resulting in the greatest rebound height?

Accepted Answer

The coefficient of restitution is calculated as:
e = √(height of rebound / height of drop)
Given this formula, it is evident that the smallest and largest values for "e" are zero (0) and one (1), which are respectively recorded when the ball does not rebound (i.e. rebound is zero) or when the ball rebounds to the height from which it was dropped.

Question 15

The conservation of linear momentum principle states that

Accepted Answer

The conservation of linear momentum represents the first impact equation and states that the total momentum possessed by a collection of objects prior to their interaction (in this case, a collision) is the same as their collective momentum after the collision.

Question 16

The coefficient of restitution will be lowest for:

Accepted Answer

Experiments show that the coefficient of restitution for various sports balls dropped onto a concrete floor range from 0.75 for a basketball or soccer ball to 0.67 and 0.32 for tennis and cricket balls, respectively. However, the coefficient of restitution is not fixed and dropping the same sports balls onto a softer surface, such as sand, reduces this value.

Question 17

One would expect a bouncing tennis ball to have a higher rebound angle than incidence angle if the contact surface applied:

Accepted Answer

In reality, the condition of a frictionless impact does not apply, as a ball will tend to slide over the surface during the time of contact. As the ball skids, frictional forces act to slow its horizontal velocity and, hence, decrease its speed in both the perpendicular and parallel directions. These higher frictional forces may lead to the ball having a higher rebound angle than its incidence angle, but this comes at the cost of a reduced velocity.

Question 18

Given the equation v'ball = vfoot * (mfoot/(mfoot + mball) * (1+e)), which of the following groupings for (i) mfoot/(mfoot + mball) and (ii) (1 + e) would result in the greatest initial velocity for the ball?

Accepted Answer

The term mfoot/(mfoot+ mball) represents the mass of the foot as a proportion of the foot and ball's combined mass. The term (1+e) represents the effectiveness of the impact, which is influenced by the hardness of the ball and the extent to which the foot deforms during impact. 
Given the two components are multiplied in the equation, the pairing that yields the greatest value would lead to the greatest initial ball velocity.

Question 19

If an elite footballer could wear heavier boots without affecting his physical performance (e.g. running speed) or kicking mechanics, how might this affect the final velocity of the ball immediately following a maximal instep kick?

Accepted Answer

The term mfoot/(mfoot+ mball) represents the mass of the foot as a proportion of the foot and ball's combined mass. Hence, adding a heavier boot to the kicking leg would increase the foot's mass, and increase the size of this term (i.e. make the foot account for a larger proportion of the combined mass of the foot and ball).

Question 20

A typical value for the term (1+e) when kicking a soccer ball is 1.5

Accepted Answer

The term (1+e) represents the effectiveness of the impact, which is influenced by the hardness of the ball (as a result of its pressure) and the extent to which the foot deforms at the ankle and metatarsophalangeal joints during impact. A typical value for this term is around 1.5.

Quiz 5: Special Topics

If an 80 kg person whose centre of mass was located 1.1 m above the ground was to maintain a rigid posture and fall forward at an angular velocity of 3.9 rad/s, calculate the moment of inertia.

Calculate the linear velocity for a rigid object that is falling forward at an angular velocity of 3.5 rad/s. Assume that the centre of mass of the object is situated at a height of 0.70 m above the ground.

Which of the following type of loading causes a material to shorten?

Which of the following type of loading causes a material to shorten on one side and lengthen on the other?

What is the stress experienced by a bone that has a tension load of 12kN applied to it over a cross-sectional area of 4 cm²?

What is the strain experienced if a 0.5 m bone is shortened to 0.498 m during compression loading?

What is 3,000,000 Pa expressed in Mega (M) Pa?

Which of the Laws of Physics is the elastic region of a stress vs strain curve an example of?

What units would the Modulus of Elasticity be measured in?

A bone sample (depth = 8 mm, width = 12 mm, length = 15 mm) failed at 335 N during tensile loading. What are the cross sectional area (CSA) and the ultimate stress for the sample. Note: use the SI units, stated in the table.

Stress is measured in N·m^-2 and strain is dimensionless

Stress is measured in N/m² and strain is represented as a proportion

Stress is measured in Pa and strain is represented as a percentage

If a collection of balls were dropped from the same height onto the same concrete surface, which of the following coefficient of restitution values would most likely correspond to the interaction resulting in the greatest rebound height?

The conservation of linear momentum principle states that

The coefficient of restitution will be lowest for:

One would expect a bouncing tennis ball to have a higher rebound angle than incidence angle if the contact surface applied:

Given the equation v'ball = vfoot * (mfoot/(mfoot + mball) * (1+e) ) , which of the following groupings for (i) mfoot/(mfoot + mball) and (ii) (1 + e) would result in the greatest initial velocity for the ball?

If an elite footballer could wear heavier boots without affecting his physical performance (e.g. running speed) or kicking mechanics, how might this affect the final velocity of the ball immediately following a maximal instep kick?

A typical value for the term (1+e) when kicking a soccer ball is 1.5

Quiz 5: Special Topics

If an 80 kg person whose centre of mass was located 1.1 m above the ground was to maintain a rigid posture and fall forward at an angular velocity of 3.9 rad/s, calculate the moment of inertia.

Calculate the linear velocity for a rigid object that is falling forward at an angular velocity of 3.5 rad/s. Assume that the centre of mass of the object is situated at a height of 0.70 m above the ground.

Which of the following type of loading causes a material to shorten?

Which of the following type of loading causes a material to shorten on one side and lengthen on the other?

What is the stress experienced by a bone that has a tension load of 12kN applied to it over a cross-sectional area of 4 cm2?

What is the strain experienced if a 0.5 m bone is shortened to 0.498 m during compression loading?

What is 3,000,000 Pa expressed in Mega (M) Pa?

Which of the Laws of Physics is the elastic region of a stress vs strain curve an example of?

What units would the Modulus of Elasticity be measured in?

A bone sample (depth = 8 mm, width = 12 mm, length = 15 mm) failed at 335 N during tensile loading. What are the cross sectional area (CSA) and the ultimate stress for the sample. Note: use the SI units, stated in the table.

Stress is measured in N·m-2 and strain is dimensionless

Stress is measured in N/m2 and strain is represented as a proportion

Stress is measured in Pa and strain is represented as a percentage

If a collection of balls were dropped from the same height onto the same concrete surface, which of the following coefficient of restitution values would most likely correspond to the interaction resulting in the greatest rebound height?

The conservation of linear momentum principle states that

The coefficient of restitution will be lowest for:

One would expect a bouncing tennis ball to have a higher rebound angle than incidence angle if the contact surface applied:

Given the equation v'ball = vfoot * (mfoot/(mfoot + mball) * (1+e) ) , which of the following groupings for (i) mfoot/(mfoot + mball) and (ii) (1 + e) would result in the greatest initial velocity for the ball?

If an elite footballer could wear heavier boots without affecting his physical performance (e.g. running speed) or kicking mechanics, how might this affect the final velocity of the ball immediately following a maximal instep kick?

A typical value for the term (1+e) when kicking a soccer ball is 1.5

What is the stress experienced by a bone that has a tension load of 12kN applied to it over a cross-sectional area of 4 cm²?

Stress is measured in N·m^-2 and strain is dimensionless

Stress is measured in N/m² and strain is represented as a proportion