Students with a weight of 400N use buckets with a weight of 10N to lift water with a weight of 10N and send it to the dormitory with a height of 5m along the stairs for use. It is useful to carry water this time. Carrying a bucket upstairs, what does it do to water?

W useful =G water h= 100N×5m=500J,

Additional work completed:

W quantity =G person h+G bucket h = 400 n× 5 m+10 n× 5 m = 2050 j.

So choose B.