Final answer:
The belief that 100 N is the exact force needed to push a 300 N box up a 1.0 m high and 3.0 m long ramp is false.
Step-by-step explanation:
The statement that a boy must have been pushing with a force of exactly 100 N while moving a box weighing 300 N up a ramp that is 1.0 m high and 3.0 m long is false. It is a common misconception that the force exerted in such a scenario is simply the weight of the object divided by the length of the ramp.
However, the actual force required to push the box up the ramp would depend on additional factors such as the inclination of the ramp, the friction between the box and the ramp, and the acceleration needed if the box is being moved at a nonzero acceleration.
In the ideal case, without friction and acceleration, the force can be calculated based on the gravitational potential energy gained by the box and the distance moved along the ramp. In this ideal calculation, the force would equal the weight times the height of the ramp divided by the length of the ramp (300 N * 1.0 m / 3.0 m), which does indeed yield 100 N.