A cart filled with sand of mass m0=50 kg is moving with constant velocity because of a constant force F=10 N acting in the direction of the cart's velocity vector. Sand starts spilling through a hole in the bottom with a constant velocity at the rate of μ=10 kg/s.. Find the velocity of the cart at the time t=4 s. Friction is to be neglected. [Take ln(5)= 1.61]