1. The problem statement, all variables and given/known data 2. Relevant equations The divergence theorem is quoted on the problem sheet. 3. The attempt at a solution I am struggling with the last question (2)c)). I have tried to put the continuity equation into the divergence theorem and have got: ∫S J.ds=-d/dt∫V ρdV But I'm not sure if I can just sub it in in this way. Do I then need to set up an intergral to get the final solution? I am not really sure what form the answer will be in. Thanks.