Q: A lever system has $$d_1 = 0.4$$\ \mathrm{m}$$ and d_2$ = 0.05\ \mathrm{m}. If $$the load is $$W = 20\ \mathrm{N}$$, what is the force $$F$$ required to balance the load?

$$F = \dfrac{20 \times 0.05}{0.4} = 2.5\ \mathrm{N}$$

Q: A person with mass $$m = 80\ \mathrm{kg}$$ stands with their center of mass $$0.12\ \mathrm{m}$$ from the pivot point. What is the torque due to their weight? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

$$T_w = 80 \times 9.8 \times 0.12 = 94.08\ \mathrm{Nm}$$

Question 1

Which condition must be satisfied for a human body to be in static equilibrium?

Accepted Answer

The vectorial sum of all forces and torques acting on the body is zero.

Question 2

A person with mass $$m = 70\ \mathrm{kg}$$ stands upright. If the distance from the pivot point to the center of mass is $$0.1\ \mathrm{m}$$ and the distance from the pivot to the point of applied force is $$1.5\ \mathrm{m}$$, what is the minimum force $$F_a$$ required to topple the person? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$F_a = \dfrac{68.6}{1.5} = 45.7\ \mathrm{N}$$

Question 3

Which of the following best describes stable equilibrium for a rigid body?

Accepted Answer

The center of mass is directly over the base of support.

Question 4

In the context of human balance, why is it important to keep the center of gravity above the feet?

Accepted Answer

To ensure the body remains in stable equilibrium and does not topple.

Question 5

A lever has a load of weight $$W at a $$distance $$d_2$$ from the fulcrum and an applied force $$F at a $$distance $$d_1$$ from the fulcrum. What is the equation for the force $$F$$ required to balance the load?

Accepted Answer

$$F = \dfrac{W d_1$}{d_2$}$$

Question 6

If a person is holding a weight in their hand with the forearm horizontal, which muscle group is primarily responsible for generating the upward force to maintain equilibrium?

Accepted Answer

Biceps muscle

Question 7

A lever system has $$d_1 = 0.4$$\ \mathrm{m}$$ and d_2$ = 0.05\ \mathrm{m}. If $$the load is $$W = 20\ \mathrm{N}$$, what is the force $$F$$ required to balance the load?

Accepted Answer

$$F = \dfrac{20 	imes 0.05}{0.4} = 2.5\ \mathrm{N}$$

Question 8

Which class of lever is represented by the human forearm when lifting a weight in the hand?

Accepted Answer

Third class lever

Question 9

A person is carrying a heavy suitcase in one hand. What must they do to maintain equilibrium?

Accepted Answer

Shift their center of gravity towards the opposite side of the suitcase.

Question 10

If the mechanical advantage $$M of a $$lever is given by $$M = \dfrac{d_2$}{d_1$}$$, what does increasing $$d_2$$ relative to $$d_1 do$$?

Accepted Answer

Increases the mechanical advantage, making it easier to lift the load.

Question 11

A person with mass $$m is $$standing upright. If the center of mass moves outside the base of support, what will happen?

Accepted Answer

The person will become unstable and may topple.

Question 12

Which of the following statements about torque is correct?

Accepted Answer

Torque is the product of force and the perpendicular distance from the pivot point.

Question 13

In a lever system, if the applied force is doubled and the distance from the fulcrum is halved, what happens to the torque produced by the applied force?

Accepted Answer

The torque remains unchanged.

Question 14

A person with mass $$m = 80\ \mathrm{kg}$$ stands with their center of mass $$0.12\ \mathrm{m}$$ from the pivot point. What is the torque due to their weight? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$T_w = 80 	imes 9.8 	imes 0.12 = 94.08\ \mathrm{Nm}$$

Question 15

Which of the following is NOT a requirement for static equilibrium?

Accepted Answer

The center of mass must be at the highest possible point.

Question 16

A person is balancing on one foot. Which factor most increases their risk of toppling?

Accepted Answer

A small base of support relative to the position of the center of mass.

Question 17

In a third class lever, which of the following is true?

Accepted Answer

The applied force is between the fulcrum and the load.

Question 18

A person lifts a weight with their forearm. If the muscle force acts at $$4\ \mathrm{cm}$$ from the elbow and the weight is held $$40\ \mathrm{cm}$$ from the elbow, what is the mechanical advantage?

Accepted Answer

$$M = \dfrac{40}{4} = 10$$

Question 19

Which scenario best illustrates unstable equilibrium?

Accepted Answer

A body with its center of mass outside its base of support.

Biophysics: Static Equilibrium, Stability, and Levers in the Human Body

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