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2.Motion in Straight Line
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A lift is coming from $8^{th}$ floor and is just about to reach $4^{th}$ floor. Taking ground floor as origin and positive direction upwards for all quantities, which one of the following is correct?
A$x < 0,v < 0,a > 0$
B$x > 0,v < 0,a < 0$
C$x > 0,v < 0,a > 0$
D$x > 0,v > 0,a < 0$
Solution
(a)As the lift is coming in downward directions displacement will be negative. We have to see whether the motion is accelerating or retarding.We know that due to downward motion displacement will be negative. When the lift reaches $4^{th}$ floor is about to stop hence, motion is retarding in nature hence, $x < 0 ; a > 0$.
As displacement is in negative direction, velocity will also be negative i.e. $v < 0$.This can be shown on the adjacent graph.
Standard 11
Physics
