you toss a coin straight up into the air. choose from the velocity-time graphs the one which describes the coin from the instant it leaves your hand until the instant it returns to your hand. assume that the positive y direction is upward.

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Not what goes around on earth but the universe too.

If the heat engine is a perfect carnot cycle engine, thenefficiency = (t2-t1)/t2   where t1=temperature of cold reservoir ( ° k) = 135            t2=temperature of hot reservoir ( ° k)   = 325thereforeefficiency = (t2-t1)/t2 = (325-135)/325 = 0.5846 = 58%  note: this is the theoretical maximum efficiency of a perfect heat engine.   real-life engines do not achieve this value.