14. The graph above shows the force on an object of mass M as a function of time. For the time interval 0 to 4 s , the total change in the momentum of the object is
(A) 40kgm/s
(B) 20kgm/s
(C) 0kgm/s
(D) −20kgm/s
(E) indeterminable unless the mass M of the object is known