Errors in experiments

The following observations were taken for determining surface tension T of water by capillary method :

diameter of capillary, $D=1.25\times10^{-2}$ m

rise of water, $h=1.45\times10^{-2}$ m.

Using $g=9.80$ m/s$^2$ and the simplified relation $T=\dfrac{rhg}2\times10^3$ N/m, the possible error in surface tension is closest to :

In an experiment to determine the acceleration due to gravity $g$, the formula used for the time period of a periodic motion is $T=2\pi\sqrt{\dfrac{7(R-r)}{5g}}$. The values of $R$ and $r$ are measured to be $(60\pm1)$ mm and $(10\pm1)$ mm, respectively. In five successive measurements, the time period is found to be 0.52 s, 0.56 s, 0.57 s, 0.54 s and 0.59 s. The least count of the watch used for the measurement of time period is 0.01 s. Which of the following statement(s) is(are) true?

A particle of mass m is acted upon by a force F given by the empirical law $F=\dfrac R{t^2}v(t)$. If this law is to be tested experimentally by observing the motion starting from rest, the best way is to plot :

A thin 1 m long rod has a radius of 5 mm. A force of 50 πkN is applied at one end to determine its Young's modulus. Assume that the force is exactly known. If the least count in the measurement of all lengths is 0.01 mm, which of the following statements is false ?