A block is placed at the top of an inclined plane and released. It slides some d

Question

A block is placed at the top of an inclined plane and released. It slides some distance down the plane while experiencing three forces: gravity, friction, and the normal force. Which of the following best describes the work done by these forces in this displacement? gravity (negetive work); friction (negative work), normal force (positive work) gravity (positive work): friction (negative work); normal force (zero work) gravity (negative work); friction (positive work); normal force (aero work) gravity (positive work), friction (negative work); nomal force (positive work gravity (positive work); friction (positive work); normal force (zero work)

Explanation / Answer

b. gravity (positive work), friction (negative work), normal force (zero work).

Gravity acts downwards and its component acts down the incline which is along the direction of motion of the block. As force and motion are in the same direction, the work done is positive. On the other hand frictional force retards the motion of the block by acting up the incline. As foce and motion are in opposite direction, the work done is negative. Lastly, normal force is perpendicular to the surface and hence perpendicular to the direction of motion. Hence the work done is zero.

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