Question 1

Which free-body diagram best represents the forces acting on a car going downhill at constant speed, as shown in the first image?

Accepted Answer

Diagram (b): Forces balanced, with one force up the slope and one down, and one perpendicular.

Question 2

Given three forces acting on a body as shown in the third image, what is the x-component of the fourth force F required to keep the body at rest?

Accepted Answer

$$-27\ 	ext{N}$$

Question 3

A toy hangs motionless at an angle in a moving train compartment. How can the apparent contradiction with Newton's Second Law be resolved?

Accepted Answer

The student is considering this situation in a non-inertial frame of reference.

Question 4

In the Atwood's Machine shown in the fourth image, what is the magnitude of the tension in the string connecting masses $$m$$ and $$5m$$?

Accepted Answer

$$\frac{5mg}{3}$$

Question 5

A car of mass $$m = 800\ 	ext{kg}$$ travels at constant speed $$v = 30\ 	ext{m/s}$$ over the top of a hill of radius $$R = 200\ 	ext{m}. $$What is the normal force acting on the car at the top of the hill?

Accepted Answer

$$4240\ 	ext{N}$$

Question 6

In the fifth image, blocks A and B are connected by a rope over a pulley. If $$m_A = 19\ 	ext{kg}$$, $$m_B = 15\ 	ext{kg}$$, $$\mu_s = 0.40$$, $$\mu_k = 0.20$$, and $$P = 60\ 	ext{N}$$, what is the maximum value of force $$Q$$ for which the system will remain at rest?

Accepted Answer

$$127\ 	ext{N}$$

Question 7

In the sixth image, a steel ball of mass $$m is $$suspended from a pair of strings. What is the tension $$T_2 in $$the horizontal string?

Accepted Answer

$$\frac{mg}{	an 	heta}$$

Question 8

A 5-gram coin lies on a wooden plank 2 m from its right edge. The plank is slowly raised and when the coin is 1.2 m above the ground, it begins to slide. What is the coefficient of static friction between the plank and the coin?

Accepted Answer

$$0.60$$

Question 9

An elevator descends a shaft at constant speed, supported by a single cable. Which statement is true about the work done by the tension and gravitational forces?

Accepted Answer

The net work done by the two forces is zero joules.

Question 10

In the seventh image, two identical masses $$M_1$$ = $$M_2 = M$ are attached to a string over a pulley. M_1$ slides up a ramp at angle $$	heta = 40.0^\circ$$ with constant acceleration a = 1.0$$\ 	ext{m/s}^2$$. What is the coefficient of kinetic friction between M_1$ and the ramp?

Accepted Answer

$$0.24$$

Question 11

Three blocks of equal mass are connected by massless strings. Block C is pulled to the right by force $$F$$, causing the system to accelerate on a frictionless tabletop. What is the tension in the string connecting blocks B and C?

Accepted Answer

$$F/3$$

Question 12

A vine of mass $$M$$ hangs from a tree, with mass distributed uniformly. What is the tension in the vine a quarter of its length above its bottom end?

Accepted Answer

$$Mg/4$$

Question 13

A 12 kg crate is pulled across a frictionless table by a cord at an angle of $$30^\circ$$ above the horizontal. If the speed increases from $$1.0\ 	ext{m/s} to$$ $$3.0\ 	ext{m/s}$$ over a distance of $$2.0\ 	ext{m}$$, what is the magnitude of the applied force $$F$$?

Accepted Answer

$$28\ 	ext{N}$$

Question 14

A 1.2 kg round of cheese is placed on a vertical spring with force constant $$k = 1800\ 	ext{N/m}$$ compressed $$15\ 	ext{cm}. $$When released, how high does the cheese rise from this position?

Accepted Answer

$$1.7\ 	ext{m}$$

Question 15

In the ninth image, an object moves a distance $$L = 1.38\ 	ext{m}$$ along the x-axis, acted upon by two forces of equal magnitude $$F = 1.41x^4$\ 	ext{N}$$, one perpendicular and one at $$45^\circ to $$the motion. What is the total work done by these two forces?

Accepted Answer

$$2.82\ 	ext{J}$$

Question 16

A fish stretches a spring by $$10\ 	ext{cm}$$ when slowly lowered. If the same fish is dropped from rest onto the spring, what is the maximum distance the spring stretches?

Accepted Answer

$$20\ 	ext{cm}$$

Question 17

An object moves along the x-axis under a conservative force described by the potential energy function $$U(x) = \alpha x^3$. What is the x-component of this force?

Accepted Answer

$$-3\alpha x^2$

Physics 140 Practice Exam 2 – Step-by-Step Guidance for Questions 1–3

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