A female cleaner slide a 200kg block up a frictionless slope (at an angle of 20

Question

A female cleaner slide a 200kg block up a frictionless slope (at an angle of 20 dgree )to the horizontal ) to a height of 2.4meters i) how much energy does she use ? ii) how much enery would a weightlifter expend if he werrw tolift the same block up to the same vertical height ? iii) how much energy would an engneer expend if they wew toslide the same block up the same slope with a coefiecient offriction (u=0.48) to avertical height of 0.4 meters ? A female cleaner slide a 200kg block up a frictionless slope (at an angle of 20 dgree )to the horizontal ) to a height of 2.4meters i) how much energy does she use ? ii) how much enery would a weightlifter expend if he werrw tolift the same block up to the same vertical height ? iii) how much energy would an engneer expend if they wew toslide the same block up the same slope with a coefiecient offriction (u=0.48) to avertical height of 0.4 meters ?

Explanation / Answer

i) energy used = mgh = 200 *9.80 * 2.4 = 4704 Joules . ii) energy used only depends on height, so same amountis used   4704Joules . iii) energy used = mgh + energy to overcomefriction = .               =   mgh + umg cos * h /sin =   .            = mgh ( 1 + u cot) = 200 *9.80 * 0.4 * (1+ 0.48 * cot20) = .              = 2938 Joules

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