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Physics Chapter 4 : Topic 1
Angles in Radians
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One radian is defined as the angle subtended at the center of a circle by an arc whose length is:
Reasoning: By definition, $\mathbf{1}$ radian is the angle subtended by an arc equal in length to the radius.
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The SI unit of plane angle is:
Reasoning: The radian is the $\mathbf{SI}$ unit for measuring plane angles.
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A complete revolution corresponds to:
Reasoning: One full circle $\mathbf{=}\mathbf{360}^{\mathbf{o}}\mathbf{= 2\pi}$ radians
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The angle $\mathbf{180}^{\mathbf{o}}$ is equal to:
Reasoning: $\mathbf{180}^{\mathbf{o}}\mathbf{= \pi}$ radians
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Which conversion factor is correct?
Reasoning: Degrees are converted to radians by multiplying by $\mathbf{\pi\ /\ 180}$.
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The angle $\mathbf{45}^{\mathbf{o}}$ equals:
Reasoning: $\mathbf{45}^{\mathbf{o}}\mathbf{=}$ $\frac{\mathbf{\pi}}{\mathbf{4}}$ $\mathbf{rad}$
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The angle $\mathbf{90}^{\mathbf{o}}$ expressed in radians is:
Reasoning: $\mathbf{90}^{\mathbf{o}}\mathbf{\times}$ $\frac{\mathbf{\pi}}{\mathbf{180}}\mathbf{=}\frac{\mathbf{\pi}}{\mathbf{2}}$
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The angle $\mathbf{60}^{\mathbf{o}}$ expressed in radians is:
Reasoning: $\mathbf{60}^{\mathbf{o}}\mathbf{\times}$ $\frac{\mathbf{\pi}}{\mathbf{180}}\mathbf{=}\frac{\mathbf{\pi}}{\mathbf{3}}$
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Which angle corresponds to $\mathbf{\pi\ /\ 6}$ radians?
Reasoning: $\frac{\mathbf{\pi}}{\mathbf{6}}\mathbf{\times}\frac{\mathbf{180}}{\mathbf{\pi}}\mathbf{=}\mathbf{30}^{\mathbf{o}}$
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The angle $\mathbf{270}^{\mathbf{o}}$ is equivalent to:
Reasoning: $\mathbf{270}^{\mathbf{o}}\mathbf{=}$ $\frac{\mathbf{3\pi}}{\mathbf{2}}$ $\mathbf{rad}$
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Which angle has a radian measure of $\mathbf{2\pi}$?
Reasoning: $\mathbf{360}^{\mathbf{o}}\mathbf{= 2\pi}$ radians
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An angle of $\mathbf{\pi\ /\ 4}$ radians is:
Reasoning: $\frac{\mathbf{\pi}}{\mathbf{4}}\mathbf{\times}\frac{\mathbf{180}}{\mathbf{\pi}}\mathbf{=}\mathbf{45}^{\mathbf{o}}$
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The angle $\mathbf{120}^{\mathbf{o}}$ in radians is:
Reasoning: $\mathbf{120}^{\mathbf{o}}\mathbf{=}$ $\frac{\mathbf{2\pi}}{\mathbf{3}}$
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The angle $\mathbf{150}^{\mathbf{o}}$ equals:
Reasoning: $\frac{\mathbf{\pi}}{\mathbf{2}}\mathbf{\ }$radians $\mathbf{=}\mathbf{90}^{\mathbf{o}}$
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Which angle corresponds to $\mathbf{\pi\ /\ 2}$ radians?
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The radian measure of $\mathbf{360}^{\mathbf{o}}$ is:
Reasoning: One complete revolution equals $\mathbf{2\pi}$ radians.
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Which expression correctly converts radians into degrees?
Reasoning: Degrees $\mathbf{= \ }$Radians $\mathbf{\times (180\ /\ \pi)}$
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The angle $\mathbf{300}^{\mathbf{o}}$ expressed in radians is:
Reasoning: $\mathbf{300}^{\mathbf{o}}\mathbf{=}$ $\frac{\mathbf{5\pi}}{\mathbf{3}}$
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Which angle corresponds to $\mathbf{2\pi\ /\ 3}$ radians?
Reasoning: $\frac{\mathbf{2\pi}}{\mathbf{3}}\mathbf{\times}\frac{\mathbf{180}}{\mathbf{\pi}}\mathbf{=}\mathbf{120}^{\mathbf{o}}$
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The angle $\mathbf{240}^{\mathbf{o}}$ is equal to:
Reasoning: $\mathbf{240}^{\mathbf{o}}\mathbf{=}$ $\frac{\mathbf{4\pi}}{\mathbf{3}}$
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An angle subtending an arc length equal to twice the radius has measure:
Reasoning: $\mathbf{\theta}\mathbf{=}$ $\frac{\mathbf{s}}{\mathbf{r}}\mathbf{=}\frac{\mathbf{2}\mathbf{r}}{\mathbf{r}}\mathbf{= 2\ rad}$
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The relation between arc length $\mathbf{(}\mathbf{s}\mathbf{)}$, radius $\mathbf{(r}\mathbf{)}$, and angle $\mathbf{(}\mathbf{\theta}\mathbf{)}$ in radians is:
Reasoning: $\mathbf{\theta}\mathbf{=}$ $\frac{\mathbf{s}}{\mathbf{r}}$ when $\mathbf{\theta}$ is in radians.
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If an arc length equals $\mathbf{\pi r}$, the subtended angle is:
Reasoning: $\mathbf{\theta}\mathbf{=}$ $\frac{\mathbf{\pi r}}{\mathbf{r}}\mathbf{= \pi\ rad}$
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An angle of $\mathbf{1}$ radian is approximately:
Reasoning: $\mathbf{1\ rad =}$ $\frac{\mathbf{180}}{\mathbf{\pi}}\mathbf{\approx}\mathbf{57.3}^{\mathbf{o}}$
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Which statement about radians is correct?
Reasoning: It is defined as a ratio of two lengths (arc length / radius).
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The angle $\mathbf{30}^{\mathbf{o}}$ in radians is:
Reasoning: $\mathbf{30}^{\mathbf{o}}\mathbf{=}$ $\frac{\mathbf{\pi}}{\mathbf{6}}$ $\mathbf{rad}$
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The angle $\mathbf{135}^{\mathbf{o}}$ is equal to:
Reasoning: $\mathbf{135}^{\mathbf{o}}\mathbf{=}$ $\frac{\mathbf{3\pi}}{\mathbf{4}}$
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The angle $\mathbf{225}^{\mathbf{o}}$ in radians is:
Reasoning: $\mathbf{225}^{\mathbf{o}}\mathbf{=}$ $\frac{\mathbf{5\pi}}{\mathbf{4}}$
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Which angle corresponds to $\mathbf{3\pi\ /\ 2}$ radians?
Reasoning: $\frac{\mathbf{3\pi}}{\mathbf{2}}\mathbf{\times}\frac{\mathbf{180}}{\mathbf{\pi}}\mathbf{=}\mathbf{270}^{\mathbf{o}}$
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A semicircle subtends an angle of:
Reasoning: A semicircle corresponds to $\mathbf{180}^{\mathbf{o}}\mathbf{= \pi}$ radians.
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A quarter circle subtends an angle of:
Reasoning: A quarter revolution is $\mathbf{90}^{\mathbf{o}}\mathbf{= \pi\ /\ 2}$ radians.
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If $\mathbf{\theta}\mathbf{= 2}$ radians and radius $\mathbf{= 5\ m}$, the arc length is:
Reasoning: $\mathbf{s}\mathbf{=}\mathbf{r}\mathbf{\ }\mathbf{\theta}\mathbf{= 5 \times 2 = 10\ m}$
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If an arc length is $\mathbf{12\ m}$ and radius is $\mathbf{4\ m}$, the angle in radians is:
Reasoning: $\mathbf{\theta =}$ $\frac{\mathbf{s}}{\mathbf{r}}\mathbf{=}\frac{\mathbf{12}}{\mathbf{4}}\mathbf{= 3\ rad}$
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Which of the following is greater?
Reasoning: $\mathbf{1\ rad \approx}\mathbf{57.3}^{\mathbf{o}}$, which is greater than $\mathbf{45}^{\mathbf{o}}$.
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Which angle is closest to $\mathbf{1}$ radian?
Reasoning: $\mathbf{1\ }$radian $\mathbf{\approx}\mathbf{57.3}^{\mathbf{o}}$
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Why are radians preferred in physics?
Reasoning: Many physical formulas $\mathbf{(e.g}$., $\mathbf{s = r\theta}$, $\mathbf{v = r\omega}\mathbf{)}$ work directly when angles are in radians.
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