NEET Physics Mathematical Tools, Units & Dimensions Question Bank Dimensions

  • question_answer
    A small steel ball of radius \[r\] is allowed to fall under gravity through a column of a viscous liquid of coefficient of viscosity \[\eta \]. After some time the velocity of the ball attains a constant value known as terminal velocity \[{{v}_{T}}\]. The terminal velocity depends on (i) the mass of the ball \[m\], (ii) \[\eta \], (iii) \[r\] and (iv) acceleration due to gravity \[g\]. Which of the following relations is dimensionally correct [CPMT 1992; CBSE PMT 1992; NCERT 1983; MP PMT 2001]

    A)    \[{{v}_{T}}\propto \frac{mg}{\eta r}\]      

    B)    \[{{v}_{T}}\propto \frac{\eta r}{mg}\]

    C)             \[{{v}_{T}}\propto \eta rmg\]

    D)               \[{{v}_{T}}\propto \frac{mgr}{\eta }\]

    Correct Answer: A

    Solution :

                     By substituting dimension of each quantity in R.H.S. of option   we get \[\left[ \frac{mg}{\eta r} \right]\ =\ \left[ \frac{M\times L{{T}^{-2}}}{M{{L}^{-1}}{{T}^{-1}}\times L} \right]\]=\[[L{{T}^{-1}}]\]. This option gives the dimension of velocity.


You need to login to perform this action.
You will be redirected in 3 sec spinner