An ideal heat engine absorbs 100 J of heat from a 400 K reservoir and releases 75 J of heat to a 200 K reservoir. How much work (in J) is done by the engine

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The anwser is: wave a has a greater pitch and frequency.

I'm having some difficulty seeing the diagram clearly.but the question says there's a net inward force on the object.so we know right away,  from newton's 2nd law of motion, thatthat baby is accelerating.  it doesn't even matter which way thenet force is pointing.  if there's any net force, then either theobject's speed or else its direction must be changing.