$A$ disc has mass $M$ and radius $R$. How much tangential force should be applied to the rim of the disc,so as to rotate with angular velocity $\omega$ in time $t$?

Elbow joint is an example of

The work function of a material is $4.0 \ eV$. The longest wavelength of light that can cause the emission of photoelectrons from this material is approximately ....... $nm$.

In an experiment on photoelectric emission from a metallic surface,the wavelength of incident light is $2 \times 10^{-7} \ m$ and the stopping potential is $2.5 \ V$. The threshold frequency of the metal (in $Hz$) is approximately (charge of electron $e = 1.6 \times 10^{-19} \ C$,Planck's constant $h = 6.6 \times 10^{-34} \ J \cdot s$):

Which pair of substances gives the same gaseous product when they react with water?

$\int_2^3 \frac{dx}{x^2-x}$ is equal to