Question 1

A car is parked on a flat road. Which of the following statements best describes the forces acting on the car according to Newton’s first law?

Accepted Answer

The net force on the car is zero, so $$\sum \vec{F} = 0$$ and the car is in equilibrium.

Question 2

A 10 kg box is pulled horizontally with a force of 40 N across a floor. The coefficient of kinetic friction between the box and the floor is $$\mu_k = 0.3. $$What is the acceleration of the box? $$(g = 9.8\, \mathrm{m/s^2$})$$

Accepted Answer

$$a = 0.86\, \mathrm{m/s^2$}$$

Question 3

Which of the following is the correct expression for the maximum static friction force acting on a body?

Accepted Answer

$$f_{s,	ext{max}} = \mu_s n$$

Question 4

A block is sliding at constant speed on a horizontal surface. Which statement is true about the forces acting on the block?

Accepted Answer

The kinetic friction force equals the applied force: $$f_k = T$$

Question 5

A skydiver of mass $$80\,\mathrm{kg}$$ reaches terminal velocity during free fall. If the drag force is proportional to velocity squared, which equation correctly describes the forces at terminal velocity?

Accepted Answer

$$D v_t^2$ = m g$$

Question 6

A ball attached to a string is whirled in a horizontal circle at constant speed. What is the direction of the net force acting on the ball?

Accepted Answer

Toward the center of the circle

Question 7

Which of the following is NOT a correct step in drawing a free-body diagram for a dynamics problem?

Accepted Answer

Including the vector $$m \vec{a} as a $$force acting on the body

Question 8

A $$5\,\mathrm{kg}$$ block rests on a horizontal surface. The coefficient of static friction is $$0.4. $$What is the minimum horizontal force required to start moving the block? $$(g = 9.8\, \mathrm{m/s^2$})$$

Accepted Answer

$$19.6\, \mathrm{N}$$

Question 9

A car rounds a flat curve of radius $$50\,\mathrm{m} at a $$constant speed of $$20\,\mathrm{m/s}. $$What is the magnitude of the net force required to keep the car moving in a circle if its mass is $$1000\,\mathrm{kg}$$?

Accepted Answer

$$8000\, \mathrm{N}$$

Question 10

Which of the following statements about friction is correct?

Accepted Answer

Kinetic friction acts when a body slides over a surface, and is given by $$f_k = \mu_k n$$

Question 11

A block is at rest on a horizontal surface. A horizontal force is gradually increased until the block just begins to move. Which of the following best describes the friction force just before the block moves?

Accepted Answer

It is equal to $$\mu_s n$$

Question 12

A $$2\,\mathrm{kg}$$ object falls under gravity with no air resistance. What is the acceleration of the object?

Accepted Answer

$$9.8\, \mathrm{m/s^2$}$$ downward

Question 13

Which of the following is a correct statement of Newton’s second law in component form?

Accepted Answer

$$\sum F_x = m a_x$$

Question 14

A block is pulled at constant velocity across a horizontal surface. If the coefficient of kinetic friction is doubled, what happens to the force required to keep the block moving at constant velocity?

Accepted Answer

It doubles

Question 15

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

Accepted Answer

Frictional force

Question 16

A ball is whirled in a circle and the string suddenly breaks. What path does the ball follow immediately after the string breaks?

Accepted Answer

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

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

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