Swift Cocos2d3.x CCSprite applyImpulse does not give the right jump

Question

I am using Cocos2d3.x with SpriteBuilder in Swift.

I want to make the animation like a bouncing ball in polls, as shown in this GIF: https://www.dropbox.com/s/43vwlbjoazaxe7u/jumpyBall_15_jul_15.gif?dl=0

If you notice in the GIF file, every second jump is half the previous jump. So it looks like 1,0,5,1,0,5,1,0,5, ...

Below are my settings:

Surveys:

Physics Enabled Density: 1.0 Static Body Collision Type: Platform 

Circle:

 Physics Enabled Density: 1.0 Dynamic Body Collision: hero Affected by gravity 

MainScene:

 func ccPhysicsCollisionBegin(pair: CCPhysicsCollisionPair!, hero: Player!, platform: Obstacle!) -> Bool { hero.physicsBody.applyImpulse(ccp(0, distanceObst)); } 

distanceObst is the distance between polls of 160.

Can someone give me suggestions on what I should do to make jumping uniform for every bounce? And I also want to speed up the races of the players, so is there any simplest way or formula or something else?