An object is moving but we don't know its mass or velocity. a force of 20 newtons to the right
is exerted on the object for 20 seconds. what is the (vector) change in linear momentum for the
body as a result of this impulse?

The impulse is (force) x (time) = (20 N) x (20 sec) = 400 N-sec

When we grind through the units, we find that the [newton-second]
is exactly the same as the [kilogram-meter/sec] unit-wise, and once
we know that, it doesn't surprise us to learn that impulse is equivalent
to a change in momentum (mass x speed ... also kg-m/s).

So this impulse exerted on the moving object adds 400 kg-m/s of
linear momentum to its motion, directed to the right.  That may or
may not be the total change in its momentum during that 20-sec,
because our 20-N may not be the only force acting on it.

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.

Aform of energy that is reflected or emitted from objects in the form of electrical and magnetic waves that can travel through space. there are many forms of  electromagnetic  energy including gamma rays, x rays, ultraviolet radiation, visible light, infrared radiation, microwaves and radio waves.