A military gun is mounted on a railroad car $(m=1500 \mathrm{kg})$ as shown in Figure P7.34. There is no frictional force on the car, the track is horizontal, and the car is initially at rest. The gun then fires a shell of mass $30 \mathrm{kg}$ with a velocity of $300 \mathrm{m} / \mathrm{s}$ at an angle of $40^{\circ}$ with respect to the horizontal. Find the recoil velocity of the car.