Q: A $$100\ \mathrm{N}$$ force is applied to a $$2.0\ \mathrm{m}$$ long steel rod with cross-sectional area $$1.0 \times 10$$^{-4}$$\ \mathrm{m^2$}. If$$ $$Y = 200 \times 10^9$\ \mathrm{N/m^2$}$$, what is the elongation $$\Delta L$$?

$$1.0 \times 10$$^{-3}$$\ \mathrm{m}$$

Q: A steel rod is compressed by a force of $$10,000\ \mathrm{N}. If $$its cross-sectional area is $$5.0 \times 10$$^{-4}$$\ \mathrm{m^2$}$$, what is the compressive stress?

$$2.0 \times 10^7$\ \mathrm{N/m^2$}$$

Question 1

A 200 kg chandelier is suspended by two cords, one making a 60° angle with the ceiling and the other horizontal. What is the tension in the angled cord? (Assume $$g = 9.8\ \mathrm{m/s^2$}.)$$

Accepted Answer

$$2260\ \mathrm{N}$$

Question 2

Which of the following is NOT a condition for an object to be in static equilibrium?

Accepted Answer

$$\sum v = 0$$

Question 3

A uniform beam of length $$20\ \mathrm{m}$$ and weight $$10,000\ \mathrm{N} is $$supported at both ends. If a $$10,000\ \mathrm{N}$$ load is placed $$10\ \mathrm{m}$$ from the left end, what is the force on the right support?

Accepted Answer

$$8,000\ \mathrm{N}$$

Question 4

A ladder of length $$5.0\ \mathrm{m}$$ and weight $$100\ \mathrm{N}$$ rests against a frictionless wall. What force must the ground exert horizontally to keep the ladder in equilibrium?

Accepted Answer

Equal to the horizontal component of the force from the wall

Question 5

Which of the following best describes stable equilibrium?

Accepted Answer

The object returns to its original position after a small displacement

Question 6

A $$1.60\ \mathrm{m}$$ steel wire with diameter $$0.20\ \mathrm{cm}$$ stretches $$0.30\ \mathrm{cm}$$ under tension. Given $$Y = 200 	imes 10^9$\ \mathrm{N/m^2$}$$, what is the tension in the wire?

Accepted Answer

$$1200\ \mathrm{N}$$

Question 7

A concrete pillar must support a $$50,000\ \mathrm{N}$$ load. If the compressive strength of concrete is $$20 	imes 10^6$\ \mathrm{N/m^2$}$$ and a safety factor of 10 is used, what is the minimum cross-sectional area required?

Accepted Answer

$$0.025\ \mathrm{m^2$}$$

Question 8

Which material has the highest Young's modulus according to the provided data?

Accepted Answer

Steel

Question 9

A beam is supported at both ends and loaded in the center. Which statement is true about the forces at the supports?

Accepted Answer

Each support carries half the total load

Question 10

A $$2.20\ \mathrm{m}$$ beam of weight $$100\ \mathrm{N} is $$held horizontally by a rope at $$30^\circ$$ above the horizontal. What is the tension in the rope if the total supported weight is $$1100\ \mathrm{N}$$?

Accepted Answer

$$2100\ \mathrm{N}$$

Question 11

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

Accepted Answer

Stress is force per unit area; strain is change in length over original length

Question 12

A stone arch is stable primarily because:

Accepted Answer

Stone is strong under compression

Question 13

If a body is in equilibrium but its center of mass is raised by a small displacement, what type of equilibrium is it in?

Accepted Answer

Unstable equilibrium

Question 14

A $$100\ \mathrm{N}$$ force is applied to a $$2.0\ \mathrm{m}$$ long steel rod with cross-sectional area $$1.0 	imes 10$$^{-4}$$\ \mathrm{m^2$}. If$$ $$Y = 200 	imes 10^9$\ \mathrm{N/m^2$}$$, what is the elongation $$\Delta L$$?

Accepted Answer

$$1.0 	imes 10$$^{-3}$$\ \mathrm{m}$$

Question 15

Which of the following is true about the net torque for an object in equilibrium?

Accepted Answer

It must be zero about any axis

Question 16

A $$10,000\ \mathrm{N}$$ beam is supported at one end and extends $$20\ \mathrm{m}$$ horizontally. What is the force at the support if a $$10,000\ \mathrm{N}$$ load is placed at the free end?

Accepted Answer

$$15,000\ \mathrm{N}$$

Question 17

Which of the following statements about the stability of an object is correct?

Accepted Answer

A lower center of mass and a broader base increase stability

Question 18

A $$100\ \mathrm{N}$$ force is applied tangentially to a disk of radius $$0.5\ \mathrm{m}. $$What is the torque produced?

Accepted Answer

$$50\ \mathrm{N \cdot m}$$

Question 19

A steel rod is compressed by a force of $$10,000\ \mathrm{N}. If $$its cross-sectional area is $$5.0 	imes 10$$^{-4}$$\ \mathrm{m^2$}$$, what is the compressive stress?

Accepted Answer

$$2.0 	imes 10^7$\ \mathrm{N/m^2$}$$

Statics: Equilibrium, Forces, and Elasticity

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