Question

Which of the following speed-time (v - t) graphs is
physically not possible?

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Answer 1

Answer:

4) all of them

Explanation:

in first and second case we see that the graph is going back in time which isn't possible.

In third one you are going in negative velocity.

Answer 2

Answer:Option 1 and 2

Explanation:

Given

Option 1 is not possible because $\frac{\mathrm{d} v}{\mathrm{d} t}$ is not differentiable at sharp edges i.e. a tends to become unrealistic so option 1 is not physically possible

While in option  3 graph is differentiable at all points so they are physically possible.

for option 2 we go back in time which is not possible.