I have entered college track and field(the field section) not long ago. And i was just wondering if the distance a thrower throws a discus affected by the mass of the thrower? Does throwing discus require momentum? If it does, is it correct to say that the more massive the thrower,the farther he can throw the object,since momentum=mass x velocity?

Yes, throwing involves momentum. But you are over simplifying it. Force = mass * velocity, but the force is the force generated by your arm and body, the mass is the mass of the discus, not you, and the velocity is the velocity of the discus. And the force is constant, so the heavier the discus, the slower it will go. But that is a bit obvious.

The correct thing to think about is conservation of momentum. The system of you an the discus can not have a net momentum. So whatever momentum you impart to the discus, the opposite momentum will be imparted to you (this is just restating Newton’s famous law: ‘for every action there is an equal and opposite reaction’). Since you assume your arm/body can produce a constant amount of energy, it makes sense that you want to limit the percentage of that energy that goes into your momentum and maximize the amount that goes into the discus. So you want your velocity after the throw to be zero. Since momentum is velocity times mass, as your mass increases, your velocity decreases. And since kinetic energy is 1/2 m v^2 = 1/2 v * momentum, as your velocity goes to zero, the percentage of the energy you generate in your throw that goes into moving you goes to zero. So the more massive you are, the more energy you will put into the discus. So you want to be as massive as possible. BUT, if your feet are firmly planted on the ground at the point of release, your effective mass will be yours plus the mass of the entire earth, since you will not slide on the ground, so to move you would mean to move the entire earth. This implies that all your energy will go into the discus (since your mass is nearly infinite in comparison to the mass of the disc). So the lesson is, no matter how much you weigh, firmly plant yourself on the ground when you release to get max distance. And if you do that, it doesn’t matter how much you weigh.

That being said, there is another issue. In hammer, there is a lot of angular momentum involved. To properly spin while throwing, you have to balance your momentum against the hammer, which means you have to lean back against the hammer to keep the hammer from pulling you out of position. The heavier you are in comparison to the hammer, the less you have to lean. And the less you have to lean, the easier it is to control yourself. And the easier it is to control yourself, the easier it is to go faster. So in hammer, there is some advantage to being heavier, just because it is easier to control yourself. There is of course a trade off since the fatter you are, the more awkward you are and the more trouble you will have controlling your body. So you don’t want to be so heavy that you have trouble moving and moving quickly. But given the same athletic prowess, the heavier thrower will have an easier time controlling themselves and the hammer. In discus, the angular momentum involved is much less, so counterbalancing a discus is not as much of an issue as it is with a hammer, but it is still somewhat of an issue. And in that aspect, weight can be an advantage.

But generally speaking, weight will not help you throw farther and the best discus throwers I knew were not the big heavy throwers, but instead, they were the tall fast people.