JEE Main & Advanced Physics Motion in a Straight Line / सरल रेखा में गति Question Bank Non-uniform Motion

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    Two cars \[A\] and \[B\] are travelling in the same direction with velocities \[{{v}_{1}}\] and \[{{v}_{2}}\]\[({{v}_{1}}>{{v}_{2}})\]. When the car \[A\] is at a distance \[d\] ahead of the car \[B\], the driver of the car \[A\] applied the brake producing a uniform retardation \[a\] There will be no collision when                                [Pb. PET 2004]

    A)             \[d<\frac{{{({{v}_{1}}-{{v}_{2}})}^{2}}}{2a}\]         

    B)             \[d<\frac{v_{1}^{2}-v_{2}^{2}}{2a}\]

    C)             \[d>\frac{{{({{v}_{1}}-{{v}_{2}})}^{2}}}{2a}\]

    D)             \[d>\frac{v_{1}^{2}-v_{2}^{2}}{2a}\]

    Correct Answer: C

    Solution :

                                Initial relative velocity\[={{v}_{1}}-{{v}_{2}}\], Final relative velocity \[=0\]             From \[{{v}^{2}}={{u}^{2}}-2as\]Þ\[0={{({{v}_{1}}-{{v}_{2}})}^{2}}-2\times a\times s\]              Þ \[s=\frac{{{({{v}_{1}}-{{v}_{2}})}^{2}}}{2a}\] If the distance between two cars is 's' then collision will take place. To avoid collision \[d>s\] \[\therefore \]\[d>\frac{{{({{v}_{1}}-{{v}_{2}})}^{2}}}{2a}\] where \[d=\] actual initial distance between two cars.


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