Question 1

A 50.0-g salt shaker is slid across a table with an initial speed of 1.15 m/s and comes to rest due to friction. If the coefficient of kinetic friction between the shaker and the table is $\mu_k = 0.25$, what is the magnitude of the frictional force acting on the shaker?

Accepted Answer

$f_k = 0.12\ \mathrm{N}$

Question 2

Which of the following best describes the role of static friction when a force is applied to an object at rest?

Accepted Answer

It adjusts up to a maximum value to prevent motion, depending on the applied force.

Question 3

A gardener uses two wires to support a pot of flowers. One wire is horizontal, and the other makes an angle of $40.0^\circ$ with the ceiling. If the pot has a mass of $2.0\ \mathrm{kg}$, what is the tension in the angled wire?

Accepted Answer

$T = \dfrac{mg}{\sin 40.0^\circ}$

Question 4

Which equation correctly expresses the force exerted by an ideal spring according to Hooke's Law?

Accepted Answer

$F = kx$

Question 5

A crate begins to slide down a tilted bed when the angle reaches $23.5^\circ$. What is the coefficient of static friction between the crate and the bed?

Accepted Answer

$\mu_s = 	an 23.5^\circ$

Question 6

A 95.0-kg crate is at rest on a ramp. If the coefficient of static friction is $\mu_s = 0.30$, what is the maximum angle $	heta$ at which the crate will remain at rest?

Accepted Answer

$	heta = \arctan(0.30)$

Question 7

A centrifuge rotates such that the bottom of a test tube moves at $v = 90.6\ \mathrm{m/s}$ and is $r = 9.25\ \mathrm{cm}$ from the axis. What is the centripetal acceleration at the bottom of the tube?

Accepted Answer

$a_c = \dfrac{v^2}{r}$

Question 8

Which statement about the tension in a real rope is correct?

Accepted Answer

Tension varies along the rope due to its weight.

Question 9

Two boxes of masses $m_1$ and $m_2$ are connected by a string and pulled by a force $F$. If the system accelerates at $a$, what is the tension $T$ in the string between the boxes?

Accepted Answer

$T = m_1 a$

Question 10

An object slides down a $3.0\ \mathrm{m}$ ramp inclined at $23^\circ$ with a coefficient of kinetic friction $\mu_k = 0.15$. How much time does it take to reach the bottom if it starts from rest?

Accepted Answer

$t = \sqrt{\dfrac{2d}{g(\sin 23^\circ - \mu_k \cos 23^\circ)}}$

Question 11

Which of the following is true about translational equilibrium?

Accepted Answer

The net force acting on the object is zero.

Question 12

A block is pulled across a rough surface at constant speed. Which statement is correct about the forces acting on the block?

Accepted Answer

The applied force equals the kinetic frictional force.

Question 13

A spring with spring constant $k = 200\ \mathrm{N/m}$ is compressed by $x = 0.05\ \mathrm{m}$. What is the magnitude of the force exerted by the spring?

Accepted Answer

$F = 10\ \mathrm{N}$

Question 14

Which of the following is NOT a property of the static frictional force?

Accepted Answer

It always equals $\mu_s N$ regardless of the situation.

Question 15

A device with three pulleys is used to apply a force to a broken leg. If the tension in the rope is $165\ \mathrm{N}$, what mass $m$ must be hung from the rope to achieve this tension? (Assume $g = 9.8\ \mathrm{m/s^2}$)

Accepted Answer

$m = \dfrac{165}{9.8}\ \mathrm{kg}$

Question 16

Which formula gives the magnitude of the centripetal force required to keep an object of mass $m$ moving in a circle of radius $r$ at speed $v$?

Accepted Answer

$F_c = m \dfrac{v^2}{r}$

Question 17

A block of mass $m$ is connected to another block of mass $M$ by a string over a frictionless pulley. If $M > m$, what is the acceleration of the system?

Accepted Answer

$a = \dfrac{(M - m)g}{M + m}$

Question 18

Which of the following statements about kinetic friction is correct?

Accepted Answer

It depends on the normal force and the coefficient of kinetic friction.

Applications of Newton’s Laws – Chapter 6 Study Notes

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