4. A block at rest is connected to a ball by a rope passing over frictionless pulleys, as shown. The goal is to determine the initial acceleration of the ball. 100 N 7.5 kg H.-0.30 30 12.5 kg a. Determine which way the 7.5 kg block is moving and place the friction force in the correct direction. Identify the forces that must be compared to determine this direction. b. Determine the acceleration of the ball.