A skateboard of negligible mass is initially at rest on a long
PHYSICS · Multi-part · CBSE · Physics · System of Particles and Rotational Motion · System of Particles and Rotational Motion
Problem
A skateboard of negligible mass is initially at rest on a long, level, frictionless surface. A student of mass 60 kg stands at the midpoint of the board and wears a 6.0 kg backpack. The board is 1.8 m long and the student initially holds the backpack directly above the midpoint of the board.
The student then slowly slides the backpack along the board until it is directly above the rear tip of the board (the tip originally behind the student). Assume no external horizontal forces act during this process.
(1) Identify the location of the center of mass of the three–object system (student, backpack, and board) relative to the board before the backpack is moved.
(2) Describe qualitatively how the position of the center of mass relative to the board changes as the backpack is moved to the rear tip.
(3) Explain whether the horizontal position of the center of mass of the system relative to the ground changes while the backpack is being moved. Justify your answer without performing numerical calculations.
(4) Predict the motion of the board relative to the ground while the backpack is being moved and provide a physical explanation for your prediction.