(a) What physical quantity is represented by the slope of a position–time (x–t) graph?
(b) What physical quantity is represented by the area under a velocity–time (v–t) graph between two instants?
(c) Explain, with reasons, what it signifies when the slope of an x–t graph becomes negative during a certain interval of time.
(d) A student claims that a negative area obtained while calculating the area under a v–t curve has no physical meaning. Give a correct explanation to refute this claim.