# Q. WHAT DO YOU MEAN BY POSITIVE, NEGATIVE AND ZERO WORK DONE. GIVE AT LEAST ONE EXAMPLE OF EACH CASE. 1. When θ is acute (<90), cosθ is positive. Hence work done is positive.

example: when a body falls freely under the action of gravity.

cos0 = 1. therefore work done by the gravity on the body falling freely is +ve.

2. When θ is acute (>90), cosθ is -ve. Hence work done is -ve.

example: when a body is thrown up, its motion is opposed by the gravity. the angle θ b/w gravitational force and displacement is 180. cos 180 = -1,  therefore work done by the gravity on a body moving upward is -ve.

3.

when, θ = 90

cos90 = 0

work done is said to be zero.

example: when a body tied to one end of a string is rotating in a circle, work done by the centripetal force applied along the string is zero because

θ = 90

cos90 = 0

• 5

we are given to do a work to displace the table. ..

1) if we diplace the table from it's place , work done is positive

2) if we can't displace the table then the work done is zero

3)if the table displace in the opposite direction of the velocity the the work done is negative

• 1

(',')
<))>
_//_ ..

• 0
What are you looking for?