Say, a body of mass 'm' is thrown at a certain angle with the vertical with certain initial velocity 'u'. The initial momentum of this object is mu. Am I right to say that if it spent 't' seconds in flight and came back, its final velocity will still be 'u'? And the change in momentum will be mu-(-mu)=2mu? And would this be correct or not: F=dp/dt =>dp=F*dt Since F=mg and dt=t, change in momentum=mgt? One of these has to be wrong. I don't know which one.