Final answer:
The claim that exactly 100 N of force is needed to push the box is false, as actual force depends on both the mechanical advantage and efficiency of the ramp. The efficiency of any simple machine is always less than 100% due to friction, making the related statement true.
Step-by-step explanation:
The statement that a boy pushing a box with a weight of 300 N up a ramp, which is 1.0 m high and 3.0 m long, must be exerting exactly 100 N of force is false. This is because the force required to push the box up the ramp depends on the mechanical advantage of the ramp and the efficiency of the ramp, which takes into account factors like friction. To calculate the force applied, one would need to consider the mechanical advantage (the ratio of the length of the ramp to its height) and the efficiency of the ramp, which is always less than 100 % due to friction.
Similarly, the statement that the efficiency of a simple machine is always less than 100 percent because some small fraction of the input work is converted to heat energy due to friction is true. No real-world machine can be completely free of friction, and even with the most well-designed systems, some work input will always be lost as heat.