Q: A 10 kg box is pulled up a $$30^\circ$$ incline by a rope with tension $$T. $$The coefficient of kinetic friction is $$\mu_k = 0.2. $$What is the expression for the net force parallel to the incline?

$$F_{\text{net}} = T - mg\sin\theta - \mu_k mg\cos\theta$$

Q: A 2 kg block slides across a rough surface and compresses a spring (with $$k = 100\ \mathrm{N/m}) by 0.2 m $$before stopping. If the block's initial speed was 2 m/s, how much energy was dissipated by friction?

$$E_{\text{fric}} = 0.4\ \mathrm{J}$$

Question 1

A 5 kg box is pushed along a frictionless horizontal surface with a constant force of 20 N. What is the acceleration of the box?

Accepted Answer

$$a = 4\ \mathrm{m/s^2$}$$

Question 2

A 2 kg object is acted upon by two forces: $$\vec{F}_1 = 6\ \mathrm{N}$$ east and $$\vec{F}_2 = 8\ \mathrm{N}$$ north. What is the magnitude of the object's acceleration?

Accepted Answer

$$a = 5\ \mathrm{m/s^2$}$$

Question 3

Which of the following best defines the acceleration due to gravity $$g at $$the surface of a planet of mass $$M$$ and radius $$R$$?

Accepted Answer

$$g = \dfrac{GM}{R^2$}$$

Question 4

A 70 kg astronaut weighs less on the Moon than on Earth. Which statement best explains why?

Accepted Answer

The Moon has less mass and a smaller radius, so $$g is $$smaller on the Moon.

Question 5

A 10 kg box is pulled up a $$30^\circ$$ incline by a rope with tension $$T. $$The coefficient of kinetic friction is $$\mu_k = 0.2. $$What is the expression for the net force parallel to the incline?

Accepted Answer

$$F_{	ext{net}} = T - mg\sin	heta - \mu_k mg\cos	heta$$

Question 6

Two blocks, $$m_1 = 3$$\ \mathrm{kg}$$ and m_2$ = 2\ \mathrm{kg}$$, are connected by a light string and pulled across a frictionless surface by a force $$F = 25\ \mathrm{N}. $$What is the tension in the string between the blocks?

Accepted Answer

$$T = 15\ \mathrm{N}$$

Question 7

A car of mass $$m$$ travels around a banked curve of radius $$r at $$speed $$v. If $$the banking angle is $$	heta$$ and there is no friction, what is the correct expression for the speed at which no friction is required?

Accepted Answer

$$v = \sqrt{rg	an	heta}$$

Question 8

A skydiver of mass $$m$$ falls through the air and eventually reaches terminal speed. Which statement best describes terminal speed?

Accepted Answer

It is the speed at which the upward resistive force equals the downward gravitational force.

Question 9

Given the resistive force $$F_r = bv$$ for a falling object, what is the expression for terminal speed $$v_t$$?

Accepted Answer

$$v_t = \dfrac{mg}{b}$$

Question 10

A force $$\vec{F}$$ acts on an object, causing a displacement $$\vec{d}. $$Which equation correctly defines the work done by the force?

Accepted Answer

$$W = \vec{F} \cdot \vec{d}$$

Question 11

A person pushes a box 5 m across a floor with a force of 40 N at an angle of $$60^\circ to $$the horizontal. What is the work done by the force?

Accepted Answer

$$W = 100\ \mathrm{J}$$

Question 12

Which of the following statements about the sign of work is correct?

Accepted Answer

Work is positive if the force and displacement are in the same direction.

Question 13

A 0.5 kg ball is dropped from a height of 10 m. Ignoring air resistance, what is its speed just before hitting the ground? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$v = 14\ \mathrm{m/s}$$

Question 14

A block of mass $$m is $$attached to a horizontal spring (spring constant $$k) $$and compressed a distance $$x$$ from equilibrium. If the block is released from rest, what is its speed as it passes through equilibrium (ignore friction)?

Accepted Answer

$$v = \sqrt{\dfrac{k}{m}}x$$

Question 15

A 2 kg block slides across a rough surface and compresses a spring (with $$k = 100\ \mathrm{N/m}) by 0.2 m $$before stopping. If the block's initial speed was 2 m/s, how much energy was dissipated by friction?

Accepted Answer

$$E_{	ext{fric}} = 0.4\ \mathrm{J}$$

Question 16

Which of the following best defines density?

Accepted Answer

$$\rho = \dfrac{m}{V}$$

Question 17

A 1.5 kg object is attached to a horizontal spring ($$k = 200\ \mathrm{N/m}) $$and is pulled 0.1 m from equilibrium. If the surface is frictionless, what is the maximum speed of the object as it passes through equilibrium?

Accepted Answer

$$v = 1.15\ \mathrm{m/s}$$

Question 18

A 60 kg person stands on a scale in an elevator accelerating upward at $$2\ \mathrm{m/s^2$}. $$What does the scale read?

Accepted Answer

$$720\ \mathrm{N}$$

Exam 2 Study Guide: Forces, Gravitation, Circular Motion, Work, and Energy

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