A group of kids noted that a car was changing velocity at a rate of -40 km/s^2. One of them said, "Something's wrong. You can't have a negative change in velocity." The second student said, "Something else is wrong. You can't have a s^2." What would you say to both kids to help them understand acceleration better?

Awind turbine is rotating counterclockwise at 0.5 rev/s and slows to a stop in 10 s. its blades are 20 m in length. (a) what is the angular acceleration of the turbine? (b) what is the centripetal acceleration of the tip of the blades at t=0s? (c) what is the magnitude and direction of the total linear acceleration of the tip of the blades at t=0s?