Question

A filmmaker wants to achieve an interesting visual effect by filming a scene through a converging lens with a focal length of 52.0 m. The lens is placed betwen the camera and a horse, which canters toward the camera at a constant speed of 7.4 m/s. The camera starts rolling when the horse is 40.0 m from the lens. Find the average speed of the image of the horse (a) during the first 2.0 s after the camera starts rolling and (b) during the following 2.0 s.