Q142 / 180 · COMEDK 2026 (9 May Shift 1) · Physics
The velocity of a body moving in a viscous medium is given by $v = \dfrac{A}{B+C}\left[1 - e^{\frac{-t}{B}}\right]$ where t is time; dimensions of A and C are
- A$[M^1L^1T^0],\ [M^0L^0T^{-1}]$
- B$[M^1L^1T^1],\ [M^0L^0T^1]$
- C$[M^0L^1T^1],\ [M^0L^0T^1]$
- Correct answerD$[M^0L^1T^0],\ [M^0L^0T^1]$
Solution
The exponent of an exponential function must be dimensionless. Therefore, the dimension of $\dfrac{t}{B}$ is $[M^0L^0T^0]$.
$[B] = [t] = [M^0L^0T^1]$
By the principle of homogeneity, quantities added or subtracted must have the same dimensions. Since $B$ and $C$ are added in the denominator, $[C] = [B] = [M^0L^0T^1]$.
The term $\left[1 - e^{\dfrac{-t}{B}}\right]$ is dimensionless. Thus, the dimensions of velocity $v$ must equal the dimensions of $\dfrac{A}{B+C}$.
$[v] = \dfrac{[A]}{[B+C]}$
$[M^0L^1T^{-1}] = \dfrac{[A]}{[M^0L^0T^1]}$
$[A] = [M^0L^1T^{-1}] \times [M^0L^0T^1] = [M^0L^1T^0]$
The dimensions of $A$ and $C$ are $[M^0L^1T^0]$ and $[M^0L^0T^1]$ respectively.
Answer: $[M^0L^1T^0],\ [M^0L^0T^1]$
$[B] = [t] = [M^0L^0T^1]$
By the principle of homogeneity, quantities added or subtracted must have the same dimensions. Since $B$ and $C$ are added in the denominator, $[C] = [B] = [M^0L^0T^1]$.
The term $\left[1 - e^{\dfrac{-t}{B}}\right]$ is dimensionless. Thus, the dimensions of velocity $v$ must equal the dimensions of $\dfrac{A}{B+C}$.
$[v] = \dfrac{[A]}{[B+C]}$
$[M^0L^1T^{-1}] = \dfrac{[A]}{[M^0L^0T^1]}$
$[A] = [M^0L^1T^{-1}] \times [M^0L^0T^1] = [M^0L^1T^0]$
The dimensions of $A$ and $C$ are $[M^0L^1T^0]$ and $[M^0L^0T^1]$ respectively.
Answer: $[M^0L^1T^0],\ [M^0L^0T^1]$
Hence, the correct answer is option: 'D'.