Problem

An intubed fan is mounted on a cart connected to a fixed wall via a linear elastic spring...

An intubed fan is mounted on a cart connected to a fixed wall via a linear elastic spring with constant k = 50 lb/ft. Assume that in a test the fan draws air at A with essentially zero speed and that the outgoing flow causes the cart to displace to the left so that the spring is stretched by 0.5 ft from its unstretched position. Assuming that the specific weight of the air γ = 7.5 × 10−2 lb/ft3 is constant, and letting the diameter of the tube at B be d = 4 ft (the cross section is assumed circular), determine the airspeed at B.