please solve question 7

Dear student,

l e t a i s t h e a c c e l e r a t i o n o f t h e \tan k . w e i g h t o f t h e w a t e r = m g f o r c e a c t i n g o n t h e w a t e r i n u p w a r d d i r e c t i o n = m' g w h e r e m' = \frac{1}{3} m t h e r e f o r e m a = m g - m' g = m g - \frac{1}{3} m g a = \frac{2 g}{3}

Regards