Box2d body setLinearImpulse() function stability

Question

I'm developing a game by Andengine for Android. Game: There is a body(let's say small box). And I want: the player collision with it, player will jump. It is jumping but not jumping the same height(in my code 100px) in every collision! My codes are here:

if (footFake.collidesWith(this))
{  

     player.getBody().applyLinearImpulse(new Vector2(0, 100/PhysicsConstants.PIXEL_TO_METER_RATIO_DEFAULT), player.getBody().getWorldCenter());

}

And the box body features:

final FixtureDef fixtureDef = PhysicsFactory.createFixtureDef(0, 0, 0);
this.body = PhysicsFactory.createBoxBody(this.mPhysicsWorld, this, BodyType.StaticBody, fixtureDef);
this.body.setUserData("jumpBox");
this.mPhysicsWorld.registerPhysicsConnector(new PhysicsConnector(this, this.body, true, true)); 

And player:

final FixtureDef fixtureDef = PhysicsFactory.createFixtureDef(0, 0, 0.1f);
this.body = PhysicsFactory.createBoxBody(this.mPhysicsWorld, this, BodyType.DynamicBody, fixtureDef);

Answer 1

Instead of applying impulse you can transform body gradually upto height you want.

And in you case body is not jumping at same height because when body collide many force applied on it. some time value of forces is same and some time it is different.

Answer 2

Applying an impulse will not always give the same height jump, because the existing velocity of the body may be different. You could use SetLinearVelocity to set the vertical velocity of the body to make sure that the starting velocity is constant every time.

Of course like Singhak has said, you should also make sure that there are no other influences (like collisions) on the body that will mess up the velocity that you want.