Estimate how long it would take one person to mow a football field using an ordinary home lawn mower. suppose that the mower moves with a 1-km/h speed, has a 0.5-m width, and a field is 360 ft long and 160 ft wide. 1 m = 3.281 ft.

10.7 hours Since we've been told that we have a speed of 1 km/h and a width of 0.5 meters that means that after 1 hour, we can mow a path 0.5 m wide and 1000 m long for a total area of 1000 m * 0.5 m = 500 m^2/hr. Now let's calculate the area of that football field. 360 ft / 3.281 ft/m * 160 ft / 3.281 ft/m = 5350.692864 m^2 Now let's divide that area by the 500 m^2 calculated earlier to see how many hours it will take. 5350.692864 m^2 / 500 m^2/hr = 10.70138573 hr So it would take about 10.7 hours to mow the football field.

Lexy is correct because angle r is between the incident wave,  n  = 0, and a diffracted wave.