1. The problem statement, all variables and given/known data A force exerts an impulse J on a particle changing its speed from u to 2u. The applied force and the initial velocity are oppositely directed along the same line. The work done by the force is-- Ans: Ju/2 2. Relevant equations Impulse= force*time impulse=change in momentum 3. The attempt at a solution Since applied force and initial velocity are oppositely directed, J=m(2u-(-u))=3mu. Work=Force*displacement=Impulse*displacement/time=Impulse*velocity But velocity is not constant. I don't know what to do from here.