Final answer:
The power used by a man to move a box is calculated using the formula P = W/t, with W being the work done (force times distance) and t the time. The answer to the provided question is 6.67 watts.
Step-by-step explanation:
To calculate the power used by a man moving a large box, we need to understand that power is the rate at which work is done or energy is transferred over time. The formula for power (P) in physics is P = W/t, where W is work done and t is time in seconds. The work done in moving an object is equal to the product of the force applied and the distance moved by that force in the direction of the force, which is given by W = Fd, where F is force in newtons and d is distance in meters.
In this particular problem, the force is equal to the weight of the box, which is 10 N. The box is moved 20 m, so the work done is 10 N * 20 m = 200 J (joules). This work is done over a period of 30 seconds. So the power used is P = 200 J / 30 s = 6.67 W (watts). Therefore, the correct answer is D. 6.67 watts.