50. A stationary object of mass $10\,\text{kg}$ is placed on a horizontal surface. The coefficient of static friction and kinetic friction between the object and the surface are $0.5$ and $0.25$ respectively. If a horizontal force of $55\,\text{N}$ is applied to the object, the net force on the object is how many newtons? $$15 \quad (1) \qquad 20 \quad (2) \qquad 30 \quad (3) \qquad 5 \quad (4)$$ %% Page 5 Physics122APage 4
A driver traveling on a rainy day at a speed of $36\ \dfrac{\text{km}}{\text{h}}$ is in motion, sees a red light and after traveling a distance of 10 meters comes to a stop. If the mass of the car is $1600\ \text{kg}$, what is the friction force between the tires and the road surface? (1) $3200$ (2) $4000$ (3) $6400$ (4) $8000$
The position–time equation of a simple harmonic oscillator in SI is $x = A\cos\dfrac{16\pi}{3}t$. At $0.5$ seconds from the start of motion, the average speed of the oscillator equals how many times its maximum speed? (1) $\dfrac{11}{3}$ (2) $\dfrac{11}{6}$ (3) $\dfrac{22}{3}$ (4) $6$
A mass $m$ is attached to a spring and this system performs simple harmonic motion with amplitude $A$, and its mechanical energy is $8\ \text{J}$. If we attach a mass equal to $\dfrac{m}{2}$ to the same spring and let it oscillate with the same amplitude $A$, the mechanical energy of this system will be how many joules? (1) $4$ (2) $8$ (3) $2\sqrt{2}$ (4) $4\sqrt{2}$
A sound source in an open space emits sound waves and the sound intensity level at a distance of 50 meters from this source is 90 dB. In this location, the average rate of sound energy transfer per square centimeter of a surface perpendicular to the direction of sound propagation is how many microwatts? $\left(I_0 = 10^{-12}\ \dfrac{\text{W}}{\text{m}^2}\right)$ (1) $10^{-1}$ (2) $10^{-2}$ (3) $10^{-3}$ (4) $10^{-4}$
A string of length $60\ \text{cm}$ and mass $6\ \text{g}$ is fixed between two points with a tension force of $324\ \text{N}$. What is the fourth harmonic frequency of the string in hertz? (1) $400$ (2) $800$ (3) $600$ (4) $1200$
In a stretched rope, one part is thin and the other part is thick. According to the figure, a pulse in the thin rope is moving toward the thick part. Which figure correctly shows the subsequent state of the rope? [Figure: A pulse moving to the right on a thin rope connected to a thick rope] (1) [Figure: transmitted pulse right, reflected pulse right on thin section] (2) [Figure: transmitted pulse right, reflected pulse left on thin section] (3) [Figure: transmitted pulse right, reflected inverted pulse left on thin section] (4) [Figure: transmitted pulse right, reflected inverted pulse left on thin section, arrows reversed]
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\textbf{50.} A stationary object of mass $10\,\text{kg}$ is placed on a horizontal surface. The coefficient of static friction and kinetic friction between the object and the surface are $0.5$ and $0.25$ respectively. If a horizontal force of $55\,\text{N}$ is applied to the object, the net force on the object is how many newtons?
$$15 \quad (1) \qquad 20 \quad (2) \qquad 30 \quad (3) \qquad 5 \quad (4)$$
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\begin{enumerate}
\setcounter{enumi}{50}
\item A driver traveling on a rainy day at a speed of $36\ \dfrac{\text{km}}{\text{h}}$ is in motion, sees a red light and after traveling a distance of 10 meters comes to a stop. If the mass of the car is $1600\ \text{kg}$, what is the friction force between the tires and the road surface?
\medskip
(1) $3200$ \hfill (2) $4000$ \hfill (3) $6400$ \hfill (4) $8000$
\item The position–time equation of a simple harmonic oscillator in SI is $x = A\cos\dfrac{16\pi}{3}t$. At $0.5$ seconds from the start of motion, the average speed of the oscillator equals how many times its maximum speed?
\medskip
(1) $\dfrac{11}{3}$ \hfill (2) $\dfrac{11}{6}$ \hfill (3) $\dfrac{22}{3}$ \hfill (4) $6$
\item A mass $m$ is attached to a spring and this system performs simple harmonic motion with amplitude $A$, and its mechanical energy is $8\ \text{J}$. If we attach a mass equal to $\dfrac{m}{2}$ to the same spring and let it oscillate with the same amplitude $A$, the mechanical energy of this system will be how many joules?
\medskip
(1) $4$ \hfill (2) $8$ \hfill (3) $2\sqrt{2}$ \hfill (4) $4\sqrt{2}$
\item A sound source in an open space emits sound waves and the sound intensity level at a distance of 50 meters from this source is 90 dB. In this location, the average rate of sound energy transfer per square centimeter of a surface perpendicular to the direction of sound propagation is how many microwatts? $\left(I_0 = 10^{-12}\ \dfrac{\text{W}}{\text{m}^2}\right)$
\medskip
(1) $10^{-1}$ \hfill (2) $10^{-2}$ \hfill (3) $10^{-3}$ \hfill (4) $10^{-4}$
\item A string of length $60\ \text{cm}$ and mass $6\ \text{g}$ is fixed between two points with a tension force of $324\ \text{N}$. What is the fourth harmonic frequency of the string in hertz?
\medskip
(1) $400$ \hfill (2) $800$ \hfill (3) $600$ \hfill (4) $1200$
\item In a stretched rope, one part is thin and the other part is thick. According to the figure, a pulse in the thin rope is moving toward the thick part. Which figure correctly shows the subsequent state of the rope?
\medskip
\textit{[Figure: A pulse moving to the right on a thin rope connected to a thick rope]}
\medskip
(1) \textit{[Figure: transmitted pulse right, reflected pulse right on thin section]} \hfill (2) \textit{[Figure: transmitted pulse right, reflected pulse left on thin section]}
(3) \textit{[Figure: transmitted pulse right, reflected inverted pulse left on thin section]} \hfill (4) \textit{[Figure: transmitted pulse right, reflected inverted pulse left on thin section, arrows reversed]}
\end{enumerate}
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\bigskip