Give reasons for

This is an application case of Newton’s Second Law. It is very intelligent act to take a long run before the jump. The key concept here is of momentum. As we know that momentum depends on the mass and velocity of the object. The athlete tries to acquire momentum as high as possible by taking a long run, by doing so he increasing his velocity which ultimately results into increment of momentum.

And momentum plays a very crucial role in long jump, as you must observe that momentum is directly proportional to the length of jump, more the momentum more the length of jump.

Hence, that is why athlete takes long run before the jump.