WHILE SLOWING TO ATTEMPT TO STOP, DEPRESSING BRAKE BECAME VERY HARD, AND CAR WOULD NOT STOP. THE ENGINE SPEED INCREASED MOMENTARILY WHILE FOOT ON BRAKE, TACHOMETER SHOWED INCREASED RPM, CAR MOVED FOWARD FASTER, AND HIT ANOTHER VEHICLE. THIS WAS 4TH TIME THIS OCCURRED WITH NEW VEHICLE, WITHIN FIRST 2000 MILES. FIRST THREE TIMES NO COLLISION OCCURRED DUE TO LUCK.