Tesla knocked $2,000 off the prices of three of its five models in the United States late Friday, another sign of the challenges facing the electric vehicle maker led by billionaire Elon Musk. The company cut the prices of the Model Y, a small SUV that is Tesla's most popular model and the top-selling electric vehicle in the U.S., and also of the Models X and S, its older and more expensive models. The cuts reduced the starting price for a Model Y to $42,990 and $72,990 for a Model S and $77,990 for a Model X. Industry analysts have been waiting for Tesla to introduce a small electric vehicle that would cost around $25,000, the Model 2. The company reported earlier this month that its worldwide sales fell sharply from January through March as competition increased worldwide, electric vehicle sales growth slowed, and earlier price cuts failed to lure more buyers.