A 2.0kg puck on perfectly frictionless ice is subjected to the following horizontal forces in four separate trials. In which trial is the puck’s acceleration exactly zero?
a) Simultaneous 4N forces directed north and east.
b) A single 3N force directed east.
c) Simultaneous 3N forces directed east and west.
d) Simultaneous 4N force directed east and 3N force directed west.