Q: Which of the following conditions must be satisfied for an object to be in static equilibrium?

$$\sum F_x = 0$$, $$\sum F_y = 0$$, $$\sum \tau = 0$$

Q: A woman sits with her lower leg stationary, and the tension in her quadriceps tendon is $$F_Q = 150\ \mathrm{N}. If $$the tendon makes an angle of $$20^\circ$$ with the horizontal, what is the vertical component of the force exerted by the tendon?

$$F_{Qy} = 150\ \mathrm{N} \times \sin(20^\circ)$$

Q: Young's modulus ($$Y) is $$defined as:

$$Y = \dfrac{\text{Stress}}{\text{Strain}}$$

Q: A steel wire of length $$L$$ and cross-sectional area $$A is $$stretched by a force $$F. If $$the wire extends by $$\Delta L$$, what is the strain in the wire?

$$\text{Strain} = \dfrac{\Delta L}{L}$$

Q: A force $$F is $$applied to a tendon with cross-sectional area $$A$$, causing it to stretch by $$\Delta L. $$Which equation gives the stress in the tendon?

$$\text{Stress} = \dfrac{F}{A}$$

Question 1

Which of the following conditions must be satisfied for an object to be in static equilibrium?

Accepted Answer

$$\sum F_x = 0$$, $$\sum F_y = 0$$, $$\sum 	au = 0$$

Question 2

A person stands facing a wall with their toes touching the wall and tries to rise onto their tiptoes. Why do they begin to topple backward?

Accepted Answer

They cannot lean forward enough to keep their center of gravity above their base of support.

Question 3

Why is it easier to carry two buckets of water, one in each hand, than a single bucket in one hand?

Accepted Answer

Carrying two buckets balances the center of gravity over the base of support, reducing the torque on the body.

Question 4

A woman sits with her lower leg stationary, and the tension in her quadriceps tendon is $$F_Q = 150\ \mathrm{N}. If $$the tendon makes an angle of $$20^\circ$$ with the horizontal, what is the vertical component of the force exerted by the tendon?

Accepted Answer

$$F_{Qy} = 150\ \mathrm{N} 	imes \sin(20^\circ)$$

Question 5

Which statement best describes the role of the center of gravity in human stability?

Accepted Answer

Stability is maintained as long as the center of gravity remains above the base of support.

Question 6

Which of the following best explains why bad posture can lead to a sore back?

Accepted Answer

Bad posture shifts the upper body's center of gravity, requiring back muscles to exert more force to maintain equilibrium.

Question 7

Young's modulus ($$Y) is $$defined as:

Accepted Answer

$$Y = \dfrac{	ext{Stress}}{	ext{Strain}}$$

Question 8

A steel wire of length $$L$$ and cross-sectional area $$A is $$stretched by a force $$F. If $$the wire extends by $$\Delta L$$, what is the strain in the wire?

Accepted Answer

$$	ext{Strain} = \dfrac{\Delta L}{L}$$

Question 9

Which of the following materials has the highest Young's modulus, based on the provided data?

Accepted Answer

Spider silk

Question 10

A spring obeys Hooke's law up to its elastic limit. What happens if the spring is stretched beyond this limit?

Accepted Answer

It will not return to its original length when the force is removed.

Question 11

A force $$F is $$applied to a tendon with cross-sectional area $$A$$, causing it to stretch by $$\Delta L. $$Which equation gives the stress in the tendon?

Accepted Answer

$$	ext{Stress} = \dfrac{F}{A}$$

Question 12

If two identical springs are connected in parallel, how does the effective spring constant $$k_{	ext{eff}}$$ compare to the spring constant $$k of $$each spring?

Accepted Answer

$$k_{	ext{eff}} = 2k$$

Question 13

A wine bottle and holder system is balanced as shown. Where should the center of gravity of the system be located for it to remain stable?

Accepted Answer

Directly above the base of support

Question 14

Which of the following best describes the difference between stress and strain?

Accepted Answer

Stress is force per unit area; strain is the fractional change in length.

Question 15

A muscle fiber is stretched by a small force and returns to its original length when the force is removed. This behavior is described as:

Accepted Answer

Elastic

Question 16

Which of the following is true about the modulus of a material?

Accepted Answer

It is a fundamental property that depends on temperature and composition.

Question 17

A bone consists of dense cortical bone on the outside and porous cancellous bone on the inside. What is the main advantage of this structure?

Accepted Answer

It provides both strength and flexibility.

Question 18

A tendon is stretched by a force and the stress-strain curve is measured. What does the slope of the linear region of this curve represent?

Accepted Answer

Young's modulus

Question 19

If a material is stretched and the change in length is proportional to the applied force, which law does it obey?

Accepted Answer

Hooke's law

Static Equilibrium, Torque, and Elasticity in the Human Body

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