Question $2\mathrm{.}1.$

As shown in Fig. $3,$ there is a cylindrical mass $M$ with a diameter of $1m$ attached to a rectangular

gate of $2m$ wide $($into the paper$).$ This gate must be opened when the water level $h$ falls below $2\mathrm{.}5$

m$.$ Determine the required mass value $M.$

Note: $(1)$ ignore the friction at the hinge and pulley; $(2)$ the cable is massless; $(3)$ tension force in

the cable acts along its length and is directed away from the object to which it is applied.