N3
ものだ
Supposed to, Should, That's the way it is
仕事は一生懸命するものだ。
Work is something you should put all your effort into.
Explanation
「ものだ」 has 3 uses
1That's how it should be
States what is normal or right: 「子供は元気に遊ぶものだ」. The negative is 「ものではない」.
仕事は一生懸命するものだ。
Work is something you should put all your effort into.
こどもは元気なものだ。
Kids are full of energy.
2Used to (looking back)
「〜たものだ」 looks back fondly on something you often did: 「子供の頃、よくこの川で泳いだものだ」.
学生の頃は、友達と朝までしゃべったものだ。
As a student, I used to talk with friends until morning.
若い頃は、よく一人で山に登ったものだ。
When I was young, I often climbed mountains alone.
3How… it is!
Expresses real feeling: 「時間が経つのは早いものだ」 (how fast time flies).
ユウキが自分からプランを立てるのは珍しいものだ。
It is rare for Yuki to plan something out on his own.
東大に入れたのか？大したもんだ。
You were able to get into Tokyo University? That is impressive.