Q: A 1500 kg car is pulled by a tow truck with a tension of 2500 N, and a friction force of 250 N opposes the motion. If the car starts from rest, what is its speed after 5.0 seconds?

$$v = \frac{(2500 - 250) \times 5}{1500}$$

Q: A 100 kg box sits in the back of a truck. The coefficient of static friction between the box and the truck bed is $$\mu_s = 0.40. $$What is the maximum acceleration the truck can have without the box slipping?

$$a_{max} = \mu_s g = 0.40 \times 9.8$$

Question 1

A 1500 kg car is pulled by a tow truck with a tension of 2500 N, and a friction force of 250 N opposes the motion. If the car starts from rest, what is its speed after 5.0 seconds?

Accepted Answer

$$v = \frac{(2500 - 250) 	imes 5}{1500}$$

Question 2

Which of the following statements about mechanical equilibrium is correct?

Accepted Answer

An object in mechanical equilibrium can be moving at constant velocity.

Question 3

A 100 kg box sits in the back of a truck. The coefficient of static friction between the box and the truck bed is $$\mu_s = 0.40. $$What is the maximum acceleration the truck can have without the box slipping?

Accepted Answer

$$a_{max} = \mu_s g = 0.40 	imes 9.8$$

Question 4

Which equation correctly represents Newton's second law for an object in equilibrium?

Accepted Answer

$$\vec{F}_{net} = \sum_i \vec{F}_i = 0$$

Question 5

A person stands on a scale in an elevator accelerating upward. Which expression gives the scale reading?

Accepted Answer

$$w_{scale} = m(g + a_y)$$

Question 6

If an object is in free fall, what is its apparent weight as measured by a scale?

Accepted Answer

$$w_{scale} = 0$$

Question 7

Which of the following best describes the difference between mass and weight?

Accepted Answer

Mass is a scalar property of matter, while weight is a force dependent on gravity.

Question 8

A box is pulled to the right by a rope but does not move. Which force opposes the pull and prevents motion?

Accepted Answer

Static friction

Question 9

When does the static friction force reach its maximum value?

Accepted Answer

When the object is about to slip

Question 10

Which formula gives the maximum static friction force?

Accepted Answer

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

Question 11

A wheel rolls without sliding on a surface. Which type of friction is acting?

Accepted Answer

Rolling friction

Question 12

Which equation correctly represents the force of kinetic friction?

Accepted Answer

$$f_k = \mu_k n$$

Question 13

A 15,000 N car is towed up a 20° slope at constant velocity. If friction is negligible, what is the tension in the tow rope?

Accepted Answer

$$T = 15,000 \sin(20^\circ)$$

Question 14

Which of the following is true about the direction of friction forces?

Accepted Answer

Friction always acts opposite to the direction of motion or expected motion.

Question 15

Which property distinguishes static friction from kinetic friction?

Accepted Answer

Static friction can vary up to a maximum value, while kinetic friction is constant during motion.

Question 16

When an object moves through a fluid, which force opposes its motion?

Accepted Answer

Drag force

Question 17

For low Reynolds number, how does the drag force depend on speed?

Accepted Answer

$$\vec{F}_{drag} \propto v$$

Question 18

What is the terminal speed of a falling object?

Accepted Answer

The speed at which $$\vec{F}_{drag} = \vec{F}_G$$

Question 19

Which of the following is NOT a limitation of the mechanical equilibrium model?

Accepted Answer

It fails for objects with constant velocity.

Question 20

A pan balance is used to measure mass. Why does gravity not affect the measurement?

Accepted Answer

Both sides experience the same gravitational force, so the value of $$\vec{g}$$ cancels out.

Dynamics I: Motion Along a Line – Force, Equilibrium, and Friction

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