Pong ball bounce

Hello i’m a new user here, i am trying to make a very simple 3d pong game, using a sphere which bounces around a rink. I can’t figure out how to make the ball continually bounce off the wall, i can only set the LinearVelocity once, in the method i make the ball in, but i don’t know how to add to its velocity in the update method.
package mygame;

import com.jme3.app.SimpleApplication;
import com.jme3.bullet.BulletAppState;
import com.jme3.bullet.collision.shapes.CollisionShape;
import com.jme3.bullet.control.RigidBodyControl;
import com.jme3.bullet.util.CollisionShapeFactory;
import com.jme3.input.MouseInput;
import com.jme3.input.controls.ActionListener;
import com.jme3.input.controls.MouseButtonTrigger;
import com.jme3.material.Material;
import com.jme3.math.Vector3f;
import com.jme3.scene.Geometry;
import com.jme3.scene.Node;
import com.jme3.scene.Spatial;
import com.jme3.scene.shape.Sphere;
import com.jme3.scene.shape.Sphere.TextureMode;

public class Main extends SimpleApplication {

public static void main(String args[]) {
Main app = new Main();
app.start();
}

private BulletAppState bulletAppState;
private Spatial scene;
private RigidBodyControl landscape;
private RigidBodyControl ball_phy;

@Override
public void simpleInitApp() {

bulletAppState = new BulletAppState();
stateManager.attach(bulletAppState);

inputManager.addMapping("shoot", 
        new MouseButtonTrigger(MouseInput.BUTTON_LEFT));
inputManager.addListener(actionListener, "shoot");
cam.setLocation(new Vector3f(5.4f,41f,-36f));
cam.lookAtDirection(new Vector3f(-0.010017181f, -0.73002344f, 0.6833487f), new Vector3f(0,1,0));

scene=assetManager.loadModel(“Scenes/newscene.j3o”);
CollisionShape sceneShape =
CollisionShapeFactory.createMeshShape((Node) scene);
landscape= new RigidBodyControl(sceneShape, 0);
scene.addControl(landscape);
bulletAppState.getPhysicsSpace().add(landscape);
rootNode.attachChild(scene);

}
private ActionListener actionListener = new ActionListener() {
public void onAction(String name, boolean keyPressed, float tpf) {
if (name.equals(“shoot”) && !keyPressed) {
makeCannonBall();
}
}
};
public void makeCannonBall() {
/** Create a cannon ball geometry and attach to scene graph. /
Sphere sphere = new Sphere(120, 120,3f);
sphere.setTextureMode(TextureMode.Projected);
Geometry ball_geo = new Geometry(“cannon ball”, sphere);
Material stone_mat = new Material(assetManager, “Common/MatDefs/Misc/Unshaded.j3md”);
ball_geo.setMaterial(stone_mat);
rootNode.attachChild(ball_geo);
/
* Position the cannon ball /
ball_geo.setLocalTranslation(new Vector3f(7.4f, -10.0f, 5.0f));
/
* Make the ball physcial with a mass > 0.0f /
ball_phy = new RigidBodyControl(1f);
/
* Add physical ball to physics space. */
ball_geo.addControl(ball_phy);
bulletAppState.getPhysicsSpace().add(ball_phy);

ball_phy.setLinearVelocity(new Vector3f(-0.6281498f, -0.778075f, -0.0052195787f).mult(50));

}

@Override
public void simpleUpdate(float tpf) {

}[/java]