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- Homework 7 mastering physics solution where's the energy solution

Amit M.

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In this problem, we will consider the following situation as depicted in the diagram (Intro 1 figure) : A block of mass slides at a speed along a horizontal, smooth table. It next slides down a smooth ramp, descending a height , and then slides along a horizontal rough floor, stopping eventually. Assume that the block slides slowly enough so that it does not lose contact with the supporting surfaces (table, ramp, or floor). You will analyze the motion of the block at different moments using the law of conservation of energy. Part A Which word in the statement of this problem allows you to assume that the table is frictionless? Top of Form Bottom of Form Although there are no truly "frictionless" surfaces, sometimes friction is small enough to be neglected. The word "smooth" often describes such low-friction surfaces. Can you deduce what the word "rough" means? Part B Suppose the potential energy of the block at the table is given by . This implies that the chosen zero level of potential energy is __________. Top of Form Bottom of Form Part C If the zero level is a distance above the floor, what is the potential energy of the block on the floor? Express your answer in terms of some or all the variables , , and and any appropriate constants. = Correct Part D Considering that the potential energy of the block at the table is and that on the floor is , what is the change in potential energy of the block if it is moved from the table to the floor? Express your answer in terms of some or all the variables , , and and any appropriate constants. = Correct As you may have realized, this choice of the zero level was legitimate but not very convenient. Typically, in such problems, the zero level is assumed to be on the floor. In solving this problem, we will assume just that: the zero level of potential energy is on the floor. Part E Which form of the law of conservation of energy describes the motion of the block when it slides from the top of the table to the bottom of the ramp? Top of Form Bottom of Form Part F As the block slides down the ramp, what happens to its kinetic energy , potential energy , and total mechanical energy ? Top of Form Bottom of Form Part G Using conservation of energy, find the speed of the block at the bottom of the ramp. Express your answer in terms of some or all the variables , , and and any appropriate constants. = Correct Part H Which form of the law of conservation of energy describes the motion of the block as it slides on the floor from the bottom of the ramp to the moment it stops? Top of Form Bottom of Form Part I As the block slides across the floor, what happens to its kinetic energy , potential energy , and total mechanical energy ? Top of Form Bottom of Form Part J What force is responsible for the decrease in the mechanical energy of the block? Top of Form Bottom of Form Part K Find the amount of energy dissipated by friction by the time the block stops. Express your answer in terms of some or all the variables , , and and any appropriate constants. = Correct Correct Correct Correct Correct Correct Correct Correct

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