Explain how can the work done be positive ,negative or zero by starting the condition in each case
Answers
Explanation:
Special cases are:
Case i) If the displacement is in the direction of force then theta is equal to 0 degree then cos0 degree equal to 1.
W=FxS. this is positive work done.
Example:
Positive work done by the force of gravity in the free fall.
Case ii)
If the displacement is normal to the direction of force that is theta is equal to 90 degree thencos 90 degree equal to zero .
W= 0.
Example:
When Coolie walk on a horizontal ground while carrying a load on his head no work is done against the force of gravity because the displacement of load is normal to the direction of force of gravity (which is vertically downward).
Note: There is two such a situation when the work done by a force is zero:
A) when there is displacement is zero .
B). when the displacement is normal to the direction of force.
Case iii).
If the displacement is in the direction opposite to force that is theta is equal to 180 degree then cos 180 degree equal to -1.
W= -FxS
Example:
When a body move on a surface, the force of friction between the body and the surface is in the direction opposite to the motion of body therefore work done by the force of friction is negative .
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