(C) Let m he mass per unit length of chain . When the velocity is `v` then a length `vdt` is brought to rest on the table in a short interval of time dt  i.e. , a mass `mvdt` i.e. a brought to rest . Hence , amount of momentum changed in time

          `dt = mvdt . v = mv^2dt`.

The force on the table due to the rate of change of falls freely , the velocity , when a length `x` has reached the table is given by `v^2 = 2gx`

Since , the weight of length `x` of the chain is `mgx`.

`:.`            Total pressure = `mgx + mv^2`

                                         = `mgx + 2mgx = 3mgx`