The two lumps of putty are moving in the opposite directions, each one encompass a speed of around 20.5 m/s. They collide and stick altogether. After the collision the joint lumps are at rest. When the mass of each and every lump was 1.50 kg before the collision, and no energy is lost to the surroundings, find out the change in mass of the system due to the collision? Take a positive answer for a raise in mass, and a negative answer for reduce in mass.