Mr Muyise wishes to use a block and tackle system to move 5bags of cement each of m ass 50kg up a tall building he is constructing. The pulley system he hopes to use consists of three pulleys in the fixed block and 2 pulleys in the movable block. His friend Mabeere advised that if the pulley system is 85% efficient, then no energy will be lost (wasted by t he machine) but he didn't understand I what his friend meant by that statement. (a)As physics student, what did Mabeere mean by that statement? (b) Explain to Mr.Muyise how energy is lost or wasted by the machine. (c) Find out how much energy Mr.Muyise must apply so as to move the cement up the b uilding

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Mr Muyise wishes to use a block and tackle system to move 5bags of cement each of m ass 50kg up a tall building he is constructing. The pulley system he hopes to use consists of three pulleys in the fixed block and 2 pulleys in the movable block. His friend Mabeere advised that if the pulley system is 85% efficient, then no energy will be lost (wasted by t he machine) but he didn't understand I what his friend meant by that statement. (a)As physics student, what did Mabeere mean by that statement? (b) Explain to Mr.Muyise how energy is lost or wasted by the machine. (c) Find out how much energy Mr.Muyise must apply so as to move the cement up the b uilding

Answer 1

(a) Mabeere meant that the pulley system is 85% efficient, so 15% of the input energy is lost due to inefficiencies like friction. This means only 85% of the input energy is effectively used to do the work. (b) Energy is lost in the machine primarily due to friction between the pulleys and the ropes, and air resistance. These factors convert some of the input energy into heat, which is not useful for lifting the cement. (c) 1. Calculate the total mass of the cement: \(5 \times 50 \text{ kg} = 250 \text{ kg}\). 2. Calculate the gravitational force: \(F = mg = 250 \text{ kg} \times 9.8 \text{ m/s}^2 = 2450 \text{ N}\). 3. Assume the height \(h\) the cement is lifted is \(h\) meters. 4. Work done to lift the cement: \(W = F \times h = 2450 \text{ N} \times h \text{ m}\). 5. Since the system is 85% efficient, the input energy \(E_{in}\) required is: \(E_{in} = \frac{W}{0.85} = \frac{2450 \times h}{0.85} \text{ J}\). Thus, Mr. Muyise must apply \(\frac{2450 \times h}{0.85} \text{ J}\) of energy to move the cement up the building.

Answer 2

(a) Mabeere meant that the pulley system is not 100% efficient, meaning some energy is lost due to factors like friction. An 85% efficiency indicates that only 85% of the input energy is used for useful work, while 15% is lost. (b) Energy is lost in the pulley system due to friction between the moving parts and air resistance. This means not all the input energy is converted into useful work. (c) To find the energy Mr. Muyise must apply, we need to calculate the work done to lift the cement and then account for the efficiency of the system.

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