adjective
BAD : I think the students will feel hopeless because they have already tried their best and failed.
GOOD : I think the students will feel disheartened because they have already tried their best and failed.
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Hopeless is usually used to describe a situation, not a person: 'The firemen tried to get the blaze under control, but it was hopeless.' When you say that a person is hopeless, you mean that they are very bad at something: 'He's hopeless at remembering names.'
To describe someone who feels that they have little or no chance of success, especially because they have already experienced failure or disappointment, use dispirited, dejected, disheartened, discouraged, despondent or demoralized : 'Having lost ten matches in a row, the team felt completely demoralized.'