Learn English – better word for “feed him”

There are a few phrases that you can use, such as in place (of), instead (of) (also stead), to express the "doing something for somebody", depending on the context.

In any case, the phrase for someone doesn't have to mean that the person you do something for must be lazy. This, again, depends on the context. Compare:

He asked me to do his assignment for him.
I offered myself to do his assignment for him.

Here are some examples of in place (of), in someone's place, instead (of), and stead, I found on the web:

John came to help in place of Max, who was sick.
When the king's cloaked challenge is answered, Fluellen stands in place of him, representing him, and receiving the blow.
She knew she should not have sent him to work in her place tonight.
"O king, take my life instead of hers. Let me die in her place," he pleaded.
... it was Judas who was crucified instead of him, ...
... she had to ask their family doctor to prescribe instead of him making it available to begin with.
Take me instead! Not my boy!
The chairman spoke in her stead.
The marketing manager was ill and her deputy ran the meeting in her stead.

So, you can say any of these followings (choose wisely, register is important),

He asked me to do his assignment for him.
He asked me to do his assignment in place of him.
He asked me to do his assignment in his place.
He asked me to do his assignment instead.
He asked me to do his assignment instead of him.
He asked me to do his assignment instead of him doing it himself.
He asked me to do his assignment in his stead. (formal)

Cow Tipping on Wikipedia notes: "Cow tipping is the purported activity of sneaking up on an unsuspecting upright cow and pushing it over for entertainment. The practice of cow tipping is generally considered an urban legend, as cows do not sleep standing up, and the implication that a cow can be pushed over and not stand up again is incorrect, as, unless injured, cows routinely lie down and can easily regain their footing. The implication that rural citizens seek such entertainment due to lack of other alternatives is also generally viewed as a stereotype."

As for the conversation, here is my attempt:

Leonard: The math is all there. It's not real.

Supplying evidence for some point and showing it isn't actual.

Penny: Yes, it is.

Rebuttal that something is real.

Sheldon: Yeah... uh, look. It is scientifically impossible for a person to tip a cow. >Even you, with your stocky build and lumberjack shoulders, you couldn't do it.

Stating that in terms of logic, it isn't realistic for a human being to push over a bovine animal. Someone with muscles and the appearance of someone that could cut down trees isn't able to accomplish this. "Lumberjack" is an occupation of someone that cuts down trees for a living often wears plaid and is thought to live in the wilderness.

Raj: It's horrible. Why would you push a cow over? They're sacred.

The Indian character noting a problem with doing this and asking what would motivate one to try this. In India, cows are considered a sacred animal that one wouldn't harm.

Penny: Oh, stop it. I've seen you eat, like, a million hamburgers.

Counter argument from the woman that has witnessed the Indian consume cow meat repeatedly.

Raj: Hey, an animal can be both sacred and delicious.

Counter to the counter-argument as he attempts to have it both ways. He wants to establish that the apparent contradiction isn't really that. "You can't have your cake and eat it" would be another phrase here.

Penny: Look, I'm telling you I've done it, okay? I clearly remember the cow standing up > >and then the cow on its side.

Clarification from the woman on the original point about pushing over a cow that she has a memory to admit as evidence.

Leonard: Were you drunk?

Question to be asked on this as if she were intoxicated, her credibility may be compromised here.

Penny: I was 16 in Nebraska. What do you think?

Obvious background point of being a teenager living in Middle America where the point is that a lot of teens may drink as there isn't much else to do.

Leonard:I think you're the one who fell over.

Explaining how the perception of the cow fell over because Penny lost control of her legs and fell down.

Penny: That would explain why the sky was also on its side.

Noting that her perspective changed as even the sky went onto the side instead of being on top.