Q: If a muscle can exert a maximum force proportional to its cross-sectional area, and the stress it can exert is $$7 \times 10^5$\ \mathrm{Pa}$$, what is the maximum force a muscle with a cross-sectional area of $$5\ \mathrm{cm}^2$$ can exert?

$$F = 3.5 \times 10^3$\ \mathrm{N}$$

Question 1

Which of the following best describes the condition for static equilibrium in a rigid body?

Accepted Answer

Both the vector sum of all forces and the vector sum of all torques acting on the body are zero.

Question 2

A person with a mass of 70 kg stands upright. If the width of their foot is 0.1 m and their height to the neck is 1.5 m, what is the minimum horizontal force applied at the shoulder required to topple them? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$F = 45.7\ \mathrm{N}$$

Question 3

Which of the following statements about the centre of gravity in the human body is correct?

Accepted Answer

It is approximately 56% of a person’s height from the soles of the feet when standing erect with arms at the side.

Question 4

A block of mass $$m$$ rests on a horizontal surface. If the coefficient of friction between the block and the surface is $$\mu$$, and the normal force is $$F_n$$, what is the magnitude of the friction force?

Accepted Answer

$$F_f = \mu 	imes F_n$$

Question 5

Which of the following is a real-world example of reducing friction by lubrication in biological systems?

Accepted Answer

Synovial fluid lubricating animal joints

Question 6

If a muscle can exert a maximum force proportional to its cross-sectional area, and the stress it can exert is $$7 	imes 10^5$\ \mathrm{Pa}$$, what is the maximum force a muscle with a cross-sectional area of $$5\ \mathrm{cm}^2$$ can exert?

Accepted Answer

$$F = 3.5 	imes 10^3$\ \mathrm{N}$$

Question 7

Which of the following best explains why friction is necessary for walking?

Accepted Answer

Friction provides the reaction force needed to push against the ground and move forward.

Question 8

A lever is defined as:

Accepted Answer

A rigid bar free to rotate about a fixed point called a fulcrum.

Question 9

Which assumption is made when analyzing joints in the body as levers?

Accepted Answer

Tendons are connected to bones at well-defined points and joints are frictionless.

Question 10

If the torque produced by an applied force $$F at a $$distance $$d$$ from the axis is given by $$L = F \cos 	heta 	imes d$$, what is the torque when $$F = 20\ \mathrm{N}$$, $$d = 0.5\ \mathrm{m}$$, and $$	heta = 60^\circ$$?

Accepted Answer

$$L = 5\ \mathrm{N\cdot m}$$

Question 11

Why does the force on the hip joint during walking exceed the body’s weight?

Accepted Answer

Because the centre of gravity is not directly above the joint, requiring greater joint force to maintain balance.

Question 12

Which of the following statements about sliding and fluid friction is correct?

Accepted Answer

Sliding friction is independent of velocity, but fluid friction has a strong velocity dependence.

Question 13

What is the main function of synovial fluid in animal joints?

Accepted Answer

To lubricate the joint and reduce frictional wear.

Question 14

A person is carrying heavy shopping bags unevenly. What does the body do to maintain balance?

Accepted Answer

The body bends and extends limbs to shift the centre of gravity back over the feet.

Question 15

Which of the following is NOT a consequence of friction in biological systems?

Accepted Answer

Friction increases the efficiency of joint movement.

Question 16

If the restoring torque due to a person’s weight is $$T_w = W 	imes 0.1\ \mathrm{m}$$ and $$W = 686\ \mathrm{N}$$, what is $$T_w$$?

Accepted Answer

$$T_w = 68.6\ \mathrm{N\cdot m}$$

Question 17

Which of the following best describes the relationship between muscle force and muscle cross-sectional area?

Accepted Answer

Muscle force is proportional to the muscle’s cross-sectional area.

Question 18

What happens to joint lubrication and cartilage as humans age?

Accepted Answer

Lubrication efficiency decreases and cartilage wears, leading to joint problems.

Question 19

Which of the following is true about the work done against friction in a joint during walking?

Accepted Answer

It is the product of the friction force and the distance over which the force acts.

Question 20

Which of the following is a correct statement about the effect of friction on moving objects?

Accepted Answer

Friction dissipates kinetic energy into heat, eventually stopping the object.

Statics, Torque, Equilibrium, Levers, and Friction in the Human Body

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