Projectiles on a horizontal plane If I projected any thing with angle $\theta$ with the horizontal on a horizontal plane, will the initial speed be equal to the final speed (neglect air resistance)?
 A: Yes the final speed is the same as the initial speed. The easiest way to think of this is using the concept of energy.
When the projectile is launched it has a certain amount of kinetic energy (KE) which depends on its speed but is independent of its direction. As it rises the projectile gains gravitational potential energy (GPE) at the expense of its KE, in such a way that the total energy is constant. As the projectile falls the GPE decreases and the KE increases back to its initial value.
GPE depends only on height, so whenever the projectile has the same height it has the same GPE. 
Speed and KE are scalar quantities which do not depend on direction. The projectile can land with the same speed as it had initially but a different velocity - ie a different direction of motion.
If we don't neglect air resistance then KE is gradually transformed into heat energy as the projectile moves through the air, both in the upward phase and the downward phase. Unlike GPE, the heat generated does not get transformed back into KE as the projectile falls, because friction is not a reversible process. When the projectile lands its GPE returns to its initial value, and some energy has been dissipated as heat energy, so the final KE - and therefore also speed - are less than at the launch. 
If we added up the heat energy, GPE and KE at the end we would find it is the same in total as at the start, because energy is always conserved.
A: 
If i projected any thing with angle theta with the horizontal on a
  horizontal plane, is the initial speed will equal to final speed (with
  neglecting air resistance)
lets say that i threw a ball with inital velocity equal 20mps with
  angle 30 with the horizontal then when the ball touches the ground is
  the final velocity equal to 20mps assuming that the plane is
  horizontal and no air resistance

I've added your follow up comment in the second paragraph above since it appears to clarify  your question.
Assuming no air drag, when the object hits the ground it will have the same horizontal component of velocity that it had when you released it. But the magnitude of the  downward vertical component of velocity when it hits the ground will be greater than the magnitude of the upward vertical component of the velocity you gave it on release. That's because the object will continue accelerating downward after passing the height of your release point, gaining additional velocity by the time it hits the ground. You should be able to calculate what the magnitude of the vertical component of velocity would be when it hits the ground.
Hope this helps.
