UNEB UCE PHYSICS 2025 ITEM 5

Students from a certain school had a trip to the hydroelectric power plant. The person in charge at the plant took them around. They at first went to see the wall of the dam. The person in charge told the students that the wall of such a dam is always built thicker and wider at the bottom than at the top. The students did not know why the wall of the dam should be built that way and feared to ask the in charge, yet they were eager to know. Later the person in charge took the students to a nearby construction site . At the site , a mixture of sand , gravel ,cement ,water and steel bars was being made to erect columns for a storeyed building . The person in charge told the students that each of the steel bars being used are of length 𝟑.𝟐𝒎 . diameter of 𝟐.𝟓𝒄𝒎 , and would stretch by 𝟎.𝟐𝒎𝒎 when a tensile force of 𝟕.𝟕𝑿〖𝟏𝟎〗^𝟓 𝑵 is applied. The students wondered whether the steel bars met the requirements for use in the structure, given the heavy weight of the building. After lunch the students visited a beach and noticed that while standing out of water , they felt a cool breeze compared to when they were sailing in a boat and wondered why the difference. One of the students quickly mentioned that there could be a number of applications of the breeze they experienced, in real life. majority of the students did not know any practical application of the breeze they experienced , since they had not yet learnt but were interested in finding out. On returning from the trip , the students approached you for help Hint : Steel bars are of good quality if the ratio of stress to strain exceeds 2.1 X 〖𝟏𝟎〗^𝟏𝟏 𝑵𝒎^(−𝟐). Task: Explain to the students why the wall they observed was designed as they observed. Help the students to determine whether the steel bars were of good quality. Explain to the students any two applications of the breeze they experienced.