Question
In a new system of units, the fundamental quantities mass, length and time are replaced by acceleration $$'a',$$ density $$'\rho '$$ and frequency $$'f'.$$ The dimensional formula for force in this system is
A.
$$\left[ {\rho {a^4}f} \right]$$
B.
$$\left[ {\rho {a^4}{f^{ - 6}}} \right]$$
C.
$$\left[ {{\rho ^{ - 1}}{a^{ - 4}}{f^6}} \right]$$
D.
$$\left[ {{\rho ^{ - 1}}{a^{ - 4}}{f^{ - 1}}} \right]$$
Answer :
$$\left[ {\rho {a^4}{f^{ - 6}}} \right]$$
Solution :
$$F = ma = \rho \,{\text{volume}}\,'a'$$
To write volume in terms of $$'a'$$ and $$'f'$$
Volume $$ = {L^3} = {\left( {\frac{L}{{{T^2}}}} \right)^3}{T^6} = {a^3}{f^{ - 6}}$$
$$\therefore F = \rho {a^4}{f^{ - 6}}$$