Physics > Test Prep > Physics Chapter 7 Test 2 ALL ANSWERS 100% CORRECT SPRING FALL-2023/24 SOLUTION AID GRADE A+ (All)

Work The product of the force and the distance moved by the force: (More generally, work is the component of force in the direction of motion times the distance moved.) W=Fd Power The time rate ... of work: (More generally, power is the rate at which energy is expended) Power = work done/time interval Energy The property of a system that enables it to do work. Mechanical Energy Energy due to the position of something or the movement of something. Potential Energy Energy that something possesses because of its position. (Stored Energy) PE = mgh Kinetic Energy Energy that something possesses because of its motion, quantified by the relationship: (Energy in Motion) Kinetic Energy = ½ mv² Work-Energy TheoremThe work done on an object equals the change in the kinetic energy of the object. (Work can also transfer other form of energy to a system) Work = ∆KE Law of Conservation of Energy Energy cannot be created or destroyed: it may be transformed from one form into another, but the total amount of energy never changes. Machine A device, such as a lever or pulley, that increases (or decreases) a force or simply changes the direction of a force. Conservation of Energy The work output of any machine cannot exceed the work input. In an ideal machine, where no energy is transformed into thermal energy, work (input) = work (output); (Fd) input = (Fd) output Lever A simple machine consisting of a rigid rod pivoted at a fixed point called the fulcrum. Efficiency The percentage of the work put into a machine that is converted into useful work output. (More generally, useful energy output divided by total energy input) 1. When is energy most evident? 1. Energy is most evident when it is changing. 2. A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, and an Impulse changes the momentum of that object. What do we call the quantity force multiplied by distance? 2. Force multiplied by distance is work. 3. Cite an example in which a force is exerted on an object without doing work on the object. 3. No work is done in pushing on a stationary wall, as in Figure 7.4. 4. Which requires more work: a) lifting a 50kg sack a vertical distance of 2m or b) lifting a 25kg sack a vertical distance of 4m?4. It is the same, for the product of each is the same; (50 kg)(2 m) = (25 kg)(4 m). 5. Exactly what is it that enables an object to do work? 5. Energy enables an object to do work. 6. If both sacks are lifted their respective distances in the same time, how does the power required for each compare? How about for the case in which the lighter sack is moved its distance in half the time? a) lifting a 50kg sack a vertical distance of 2m or b) lifting a 25kg sack a vertical distance of 4m? 6. The same power when both are raised in the same time; Twice the power for the lighter sack raised in half the time. 7. A car is raised a certain distance in a service station lift and therefore has potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have? 7. It would have twice because distance raised is twice. 8. Two cars are raised to the same elevation. If one car is twice as massive as the other, compare their gains of potential energy. 8. Twice-as-massive car has twice the PE. 9. When is the potential energy of something significant? 9. PE is significant when it changes, does work or transforms to energy of another form. [Show More]

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