Question 1

A gymnast hangs motionless from a rope attached to the ceiling. The gymnast's weight is 500 N, the rope's weight is 100 N, and the O-ring's weight is 50 N. What is the tension at the lower end of the rope (just above the gymnast)?

Accepted Answer

$$T_1 = 500$$\ \mathrm{N}$$

Question 2

Which of the following is the correct mathematical condition for equilibrium of an object in two dimensions?

Accepted Answer

$$\sum F_x = 0$$ and $$\sum F_y = 0$$

Question 3

A car engine of weight $$w = 2200\ \mathrm{N} is $$suspended as shown in the diagram by three chains. If the angle between the ceiling chain and the horizontal is $$60^\circ$$, what is the tension in the chain attached to the ceiling?

Accepted Answer

$$T_3 = 2540$$\ \mathrm{N}$$

Question 4

A block of mass $$m$$ slides down a frictionless incline at angle $$\alpha. $$What is the acceleration of the block?

Accepted Answer

$$a = g \sin \alpha$$

Question 5

A box is pulled across a horizontal surface at constant speed. If the coefficient of kinetic friction is $$\mu_k$$ and the normal force is $$n$$, what is the magnitude of the frictional force?

Accepted Answer

$$f_k = \mu_k n$$

Question 6

A 600 N person stands on a scale in an elevator accelerating upward at $$2.0\ \mathrm{m/s^2$}. $$What does the scale read? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$n = 724\ \mathrm{N}$$

Question 7

Which of the following statements about static friction is correct?

Accepted Answer

Static friction can vary up to a maximum value $$f_s \leq \mu_s n.$$

Question 8

A block is at rest on a horizontal surface. Which of the following is true about the forces acting on the block?

Accepted Answer

The normal force equals the weight of the block.

Question 9

Which of the following is NOT a correct application of Newton’s laws in a free-body diagram?

Accepted Answer

Including $$m \vec{a} as a $$force vector.

Question 10

A car is moving at constant velocity on a straight road. Which statement is true about the net force acting on the car?

Accepted Answer

The net force is zero.

Question 11

A block is being pulled with a force $$T on a $$rough surface and just begins to move. Which equation correctly describes the maximum static friction force?

Accepted Answer

$$f_s = \mu_s n$$

Question 12

Which of the following best describes the difference between static and kinetic friction?

Accepted Answer

Static friction prevents motion up to a maximum value; kinetic friction acts during motion and is usually less than maximum static friction.

Question 13

A skydiver reaches terminal velocity during free fall. Which statement is correct?

Accepted Answer

The upward force of air resistance equals the downward force of gravity.

Question 14

Which of the following is NOT a fundamental force of nature?

Accepted Answer

Frictional force

Question 15

A ball is whirled in a horizontal circle on a string. If the string breaks, what path does the ball follow?

Accepted Answer

It moves in a straight line tangent to the circle at the point of release.

Question 16

Which equation gives the net force required to keep a mass $$m$$ moving at speed $$v in a $$circle of radius $$R$$?

Accepted Answer

$$F_{net} = \frac{m v^2$}{R}$$

Question 17

Which of the following best explains why lubricating oil reduces friction between two surfaces?

Accepted Answer

It forms a film that separates the surfaces, reducing molecular interactions.

Question 18

A block is sliding at constant speed on a horizontal surface. Which of the following statements is true?

Accepted Answer

The applied force equals the kinetic friction force.

Question 19

Which of the following is a correct statement about the coefficient of friction?

Accepted Answer

It depends on the materials and surfaces in contact.

Applying Newton’s Laws: Equilibrium, Dynamics, and Friction

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