Final answer:
The useful work done when pushing a 50 kg box with force of 20N along a rough surface for 5m, experiencing a frictional force of 10N, is 50 Joules.
Step-by-step explanation:
In this question, we are asked to calculate the useful work done. The concept of work in Physics is defined as force times distance. However, in this case, we have friction acting against the motion. Therefore, the useful work done will be the work done against friction only. The box is pushed with a force of 20N and the frictional force is 10N. The useful work done is obtained by subtracting the work done against friction from the total work done.
The formula for work is: Work = Force x Distance. Hence, the total work done = 20N * 5m = 100 Joules. The work done against friction = Frictional force x Distance = 10N * 5m = 50 Joules.
Therefore, the useful work done = Total work - Work done against friction = 100 Joules - 50 Joules = 50 Joules.
Learn more about Useful Work Done