无力

He is unable to accomplish the task within two months.

feeble resistance

have weak leadership

be unable to support the family

be unable to fulfil the production quotas

be powerless to fight back

have no strength to spare

be powerless to resist a temptation

be outside/beyond one's power to help

He was feeble from a long illness.

lack the strength to stand up

speak in a feeble/weak voice

feel weak in one's legs/limbs

feel weak all over