Final answer:
The boy's assumption that a force of 100 N was needed is false because it oversimplifies the situation and neglects other factors such as friction and ramp efficiency.
Step-by-step explanation:
The question is addressing a scenario involving a boy pushing a box up a ramp and the associated forces. To determine if the statement 'A boy pushed a box with a weight of 300 N up a ramp. He said that, because the ramp was 1.0 m high and 3.0 m long, he must have been pushing with force of exactly 100 N' is true or false, we need to understand the concept of work done against gravity and the mechanical advantage of using a ramp.
Work done is calculated as the force applied times the distance moved in the direction of the force. The weight of the box (300 N) represents the gravitational force acting on it. The ramp provides a mechanical advantage because it allows the box to be lifted a smaller force over a longer distance. However, this does not mean that the force applied is necessarily one third of the weight just because the ramp is three times as long as it is high. The actual force needed will also depend on additional factors such as friction between the ramp and the box.
Therefore, the boy's statement that he must have been pushing with exactly 100 N of force is false. The actual force required can only be precisely determined by taking all forces into account, including friction and the efficiency of the ramp.