Efficiency of Machines Quick Check Answers - Physical Science B
Which is the equation for a machine’s efficiency?
ANSWER - Efficiency=output energy (on top of) input energy ⋅ 100
A rotating space heater used 1,400 joules of energy while heating a room. Of that total, 896 joules produced thermal energy, 181 joules produced kinetic energy, 203 joules produced light energy, and 120 joules produced sound energy. What is the space heater’s efficiency?
ANSWER - 64%
Lenore is on an inclined plane next to her truck. Holding her hands steady, she pushes a box up the plane and into her truck. Where can energy be lost?
ANSWER - Friction between the box and the inclined plane.
Ronald pushes a box up an inclined plane with 35% efficiency. If 224 joules of energy went into moving the box, how much energy did Ronald put into the inclined plane?
ANSWER - 640 joules
1000 joules of energy are put into a pulley system, and 400 joules come out. What does the Law of Conservation of Energy imply about the lost energy?
ANSWER - The lost energy is not truly lost, but it changed into a different form.
To find the efficiency of a machine, you need to use the equation: Efficiency = (output energy / input energy) * 100.
For the first question, the equation for a machine's efficiency is Efficiency = (output energy / input energy) * 100. In this case, the output energy is the total amount of energy used by the rotating space heater, which is 1400 joules. The input energy is the sum of the different types of energy produced, which is 896 joules + 181 joules + 203 joules + 120 joules = 1400 joules. Therefore, using the formula, the efficiency is (1400 / 1400) * 100 = 100%. So the space heater's efficiency is 100%.
For the second question, energy can be lost due to friction between the box and the inclined plane. As Lenore pushes the box up the inclined plane, the friction between the box and the plane converts some of the input energy into heat and sound energy, causing energy loss.
For the third question, the problem states that Ronald has a 35% efficiency. This means that the output energy is 35% of the input energy. We are given that 224 joules of energy went into moving the box, so we can set up the equation: 35% = 224 joules / input energy. Rearranging the equation, we can solve for the input energy: input energy = 224 joules / (35% / 100%) = 640 joules. Therefore, Ronald put 640 joules of energy into the inclined plane.
For the fourth question, the Law of Conservation of Energy implies that the lost energy is not truly lost, but it changed into a different form. In this case, the pulley system received 1000 joules of energy as input, but only 400 joules came out as output. The 600 joules of energy that are unaccounted for are not lost forever, but they were converted into some other form, such as heat, sound, or mechanical energy.