An object is placed on the surface of a smooth inclined plane of inclination 𝜃 . It takes time t to reach the bottom . If the same object is allowed to slide down a rough inclined plane of same inclination 𝜃 , so as to move the same distance , it takes time ‘nt’ to reach the bottom where n is a number greater than 1 . The coefficient of friction 𝜇 𝑖𝑠 𝑔𝑖𝑣𝑒𝑛 𝑏𝑦 : 𝜇 = tan⁡𝜃 (1 - 1/𝑛^2 ) 𝜇 = cot⁡𝜃 (1 - 1/𝑛^2 ) 𝜇 = tan⁡𝜃 〖"(1 - " 1/𝑛^2 ")" 〗^(1/2) 𝜇 = cot⁡𝜃 〖"(1 − " 1/𝑛^2 ")" 〗^(1/2)