In an ice rink, a 60kg skater stands on a 20kg wheeled platform that rolls without friction on the ice. The skater pulls horizontally on a rope attached to a fixed post so that the rope tension is 80N.
\nFor each of the following system choices, state whether the 80N rope force is internal or external to the system and indicate whether the horizontal acceleration of that system’s center of mass is zero or non-zero.
(i) the skater alone
(ii) the skater plus platform together