Question and my approach are in attachments please someone help me out of my confusion??(basic kinematics)
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Answers
Explanation for first doubt:
A ball is thrown vertically upwards with an initial velocity, u. It reaches a maximum height and then falls back. Acceleration due to gravity is g, and displacement is s.
From laws of linear motion , we know that
v² = u² + 2gs
At the top most point v = 0
therefore,
0 = u² + 2gs
g = - u²/2s
From above equation it is evident that sign of g depends on displacement s, and we know that displacement depends on selection of reference point.
Therefore, if displacement from ground to maximum height is taken as positive then the acceleration due to gravity will be negative. Similarly, if the displacement from ground to maximum height is taken as negative then then the acceleration due to gravity will be positive.
Thus, we can conclude that the acceleration due to gravity should be taken as positive or negative based on the reference point of displacement.
Explanation for second doubt:
For a object thrown upwards, we expect a negative slope. Also, at a time when the object reaches maximum height, velocity should be zero. Hence, the graph is as shown in figure D.