2019-03-01_Physics_Times

4. Work done in different cases

(Area = Work done with Variable Force)

(I) An object of mass m is lifted to a height h (<<
radius of earth) above the ground in air without
any acceleration (uniform velocity)
Work done by lifting force W Fh mghF 

Work done by the gravitational force is

Wg mgh

Work done by resultant force is zero

(II) Work done in elongating a spring of spring

constant K from x 1 to x 2 is

 

2 2

2 1

1

2

W K x x .