title: Change direction of a moving object....(pure physic question)
body: <p>This is  a pure physic question but i don't know why it doesn't work....i have  a moving object.i get the value of vcos(theta) and vsin(theta)...from this i calculate the velocity and angle of motion.....also i know another point (x,y) and want to direct the object to this point.I think i need to apply a certain force(force must have X and Y axis value)to direct the object towards the point....so to get the amount of force required i just follow
  the formula:</p>
  
  <p>fX=V2cos(theta2)-V1cos(theta1)
  fY=V2sin(theta2)-V1sin(theta1)</p>
  
  <p>no matter what ever the syntex are given bellow(i give it for those people know objective c).........my equation doesn't work.....can anyone help......</p>
  
  <pre><code>    if (acceleration.x&gt;1.5 || acceleration.y&gt;1.5) {
  
              shakeCounter++;
              [_label setString:[NSString stringWithFormat:@"%d",shakeCounter]];  
  
  
          //get the velocity of moving object.......................  
          b2Vec2 mVelik = ballBody-&gt;GetLinearVelocityFromLocalPoint(localPoint);
  
  
          float angleOfCurrentDirectionOfMotion;
          float angleOfDesiredDirectionOfMotion;
           //calculate first velocity
          float V1=sqrt(pow(mVelik.x, 2)+pow(mVelik.y, 2));
          //calculate second velocity
          float V2=V1+factor;
          //calculate current  angle
          angleOfCurrentDirectionOfMotion=atan(mVelik.y/mVelik.x);
           //calculate desired angle
          angleOfDesiredDirectionOfMotion=atan(acceleration.y/acceleration.x);
  ///calculate FX and FY
          float X=V2*cos(angleOfDesiredDirectionOfMotion)-V1*cos(angleOfCurrentDirectionOfMotion);
          float Y=V2*sin(angleOfDesiredDirectionOfMotion)-V1*sin(angleOfCurrentDirectionOfMotion);
  
          b2Vec2 force = b2Vec2(X,Y);
  
   ///apply Force to change direction....   
          ballBody-&gt;ApplyForce(force, ballBody-&gt;GetPosition());
  
  }
  </code></pre>