The question says that the students pull the string steadily. WE assume that this means that the string is being puled at steady rate. Also we will need to assume that the effect to evaporation of dry ice into carbon dioxide is negligible.
Based on these assumptions the answerer
are as follows:
Forces acting on the block:
All the four forces, that is towing force, a normal force, kinetic friction, andthe force of gravity will act on the block. However the resultant force will be zero as towing force will be cancelled out by the kinetic friction, and force of gravity will be cancelled out by a normal force which is equal and opposite of gravitational force.
Motion of the block while it is on the table:
The block will move at constant speed equal to the rate at which the string is being pulled. However is must be noted that when the student just starts pulling on the block, the rate of pulling for a split second will be accelerating from zero to steady state. We are not considering this initial situation for any part of the question.
Forces acting on the block after it leaves the table:
The force of gravity. The block will fall with accelerating speed under the influence of this force.
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