Q. 2 E4.1( 9 Votes )

Choose one or more correct alternatives.

While dragging or lifting an object, negative work is done by

i. the applied force

ii. gravitational force

iii. frictional force

iv. reaction force

Answer :

Option (ii) gravitational force and (iii) Frictional Force

Explanation:


Work done by a force on an object is negative when direction of force acting on object and displacement of object are in exactly opposite direction, or direction of displacement makes 1800 with direction of applied force because we know work done on an object due to a force is given by relation


W = F× s × cos𝜽


Where W is the work done due to force F in displacing object by S , 𝜽 is the angle between force and displacement.


angle between force and displacemnt is


𝜽 = 1800


So, work done will be


W = F× s × cos1800


From trigonometry we know, cos1800 = -1


So putting the value we get work done as


W = -FS


i.e. work done is negative when direction of displacement and applied force are opposite


Now when an object is lifted from ground, gravitational force due to earth in acting in downward direction and displacement is in upward direction due to applied force


as Shown in figure



Since Gravitational force and direction of displacement are in opposite direction work done by gravitational force is negative


Now when an object is dragged Frictional force is trying to oppose the motion and hence acts in direction of applied force and displacement


As shown in figure



As displacement of object and applied frictional force are in opposite direction work done by frictional force is negative.


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