The apparatus is initially at rest on a nearly frictionless surface. Then you pull the string with a constant force . At the instant when the center of the disk has moved a distance , an additional length of string has unwound off the disk. (Use any variable or symbol stated above as necessary.) (a) At this instant, what is the speed of the center of the apparatus? Entry field with correct answer Edit Explain your approach. Entry field with incorrect answer now contains modified data I applied the Energy Principle to the system as an extended object. I applied the Energy Principle to the system as a point particle. I applied the Energy Principle to the disk only. I applied the Energy Principle to the small masses only. (b) At this instant, what is the angular speed of the apparatus? Entry field with incorrect answer Edit Explain your approach. Entry field with incorrect answer I applied the Energy Principle to the system as a point particle. I applied the Energy Principle to the small masses only. I applied the Energy Principle to the system as an extended object. I applied the Energy Principle to the disk only.