Problem #$8[10$ marks$]$ Suppose a clay model of a koala bear has a mass of $0\mathrm{.}200$ kg and slides on ice at a speed of $0\mathrm{.}750$ m$/$s$.$ It runs into another clay model, which is initially motionless and has a mass of $0\mathrm{.}350$ kg$.$ Both being soft clay, they naturally stick together. $($a$)$ What is their final velocity? $($b$)$ What percentage of the initial kinetic energy remains after this collision?