Question

if work done by a body is 16830erg if it mass and velocity is decresed by1/2 and then increased by 3/7 then the energy acting up on it in joules and if you don't know answer for this please follow me and I will ask many more questions for you to increase your knowledge

Answer 1

The wordings are not at all clear. However, I do that sum by assumptions.

W = 16, 380 erg.

After the work is done, the body attains KE equal to W.
So  1/2 m v² = W

  If mass decreased by 1/2, it becomes m/2.  If speed v is increased by 3/7 then it becomes v * 10/7 = 10* v/7. 

     New Energy = 1/2 * 5m/7 * [ 10 v/7]² 
                           = (500 / 343) * 1/2 * m v²

    It is an increase of  157/343 th of W.
    Increase = 157 / 343  * 16, 830 ergs
                   = 7, 703.5 ergs
                   = 7.7035 * 10⁻⁴ Joules.        1 J = 10⁷ ergs.

Answer 2

W = 16, 380 erg.

After the work is done, the body attains KE equal to W.

So  1/2 m v² = W

 then it becomes v * 10/7 = 10* v/7. 

    New Energy = 1/2 * 5m/7 * [ 10 v/7]² 

                          = (500 / 343) * 1/2 * m v²

   It is an increase of  157/343 th of W.

   Increase = 157 / 343  * 16, 830 ergs

                  = 7, 703.5 ergs

                  = 7.7035 * 10⁻⁴ Joules.        1 J = 10⁷ ergs