a variable force is exerted on a body of constant mass. the body initially at rest moves in a straight line. the following graph shows how the force varies with time. All frictional force are ignored. if the velocity of the object is 7m/s after 2 sec. the velocity after 3.4 sec will be approx. a)11.9 m/s b)20.2 m/s c)17 m/s d)28.9 m/s Please explain