Identify the physical quantity that has the unit $N\,m^{-1}\,s^{-2}$.

Which of the following pairs does not have the same dimensions?

The mechanical equivalent of heat $J$ is

In the context of accuracy of measurement and significant figures in expressing results of experiment,which of the following is/are correct?
$(1)$ Out of the two measurements $50.14 \, cm$ and $0.00025 \, A$,the first one has greater accuracy.
$(2)$ If one travels $478 \, km$ by rail and $397 \, m$ by road,the total distance travelled is $478 \, km$.

Match List-$I$ with List-$II$ and choose the correct answer from the options given below:

List-$I$	List-$II$
$A$. Boltzmann constant	$I$. $[M^{-1}L^3T^{-2}]$
$B$. Stefan's constant	$II$. $[ML^2T^{-1}]$
$C$. Planck's constant	$III$. $[ML^2T^{-2}K^{-1}]$
$D$. Gravitational constant	$IV$. $[ML^0T^{-3}K^{-4}]$

The density of a solid ball is to be determined in an experiment. The diameter of the ball is measured with a screw gauge,whose pitch is $0.5 \ mm$ and there are $50$ divisions on the circular scale. The reading on the main scale is $2.5 \ mm$ and that on the circular scale is $20$ divisions. If the measured mass of the ball has a relative error of $2 \%$,the relative percentage error in the density is (in $\%$)