A body of mass 4 kg is projected vertically upward with an initial velocity 40 meters per second. We assume that the forces acting on the body are the force of gravity and a retarding force of air resistance with direction opposite to the direction of motion and with magnitude clv(t)| where c = 0.4 and v(t) is the velocity of the ball at time t. The gravitational constant is g = 9.8m/s. a) Find a differential equation for the velocity v: dv (-9.8) - V dt b) Solve the differential equation in part a) and find a formula for the velocity at any time t: v(t) =