12. For each of the situations given, state whether frictional forces do positiv
ID: 776505 • Letter: 1
Question
12. For each of the situations given, state whether frictional forces do positive, negative, or zero work on the italicized object. (a) A plate slides across a table and is brought to rest by fric- tion. (b) A person pushes a chair at constant speed across a rough, horizontal surface. (c) A box is set down on a stationary conveyor belt. The conveyor belt is then turned on and the box begins to move, being carried along by the belt. (d) A person exerts a horizontal force on a banana at rest on a counter top. The banana remains at rest.Explanation / Answer
(a) Workdone by Frictional force is negative in the case of A plate slides along a table and brought to rest,as the force retards the body.
Frictional Force is opposite to the direction of motion.Here workdone by frictional force(which is negative) balances with workdone by gravity to make the plate rest.
(b)Workdone is positive.
Person pushes the chair at constant speed on rough horizontal surface.As there is relative motion between the rough surface and the chair, the workdone by ths frictional force converted into kinetic energy of the chair.
(c)Workdone in case of box settled down on converer belt is zero.
As there is no relative motion between box and belt.Frictional forces arises due to relative motion,which is absent in this case
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