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Question

Two cars A and B are travelling in the same direction with velocities v subscript A end subscriptand v subscript B end subscript left parenthesis v subscript A end subscript greater than v subscript B end subscript right parenthesis. When the car A is at a distance s behind car B, the driver of the car A applies the brakes producing a uniform retardation a, there will be no collision when

  1. s less than fraction numerator open parentheses v subscript A end subscript minus v subscript B end subscript close parentheses to the power of 2 end exponent over denominator 2 a end fraction  
  2. s equals fraction numerator open parentheses v subscript A end subscript minus v subscript B end subscript close parentheses to the power of 2 end exponent over denominator 2 a end fraction  
  3. s greater or equal than fraction numerator open parentheses v subscript A end subscript minus v subscript B end subscript close parentheses to the power of 2 end exponent over denominator 2 a end fraction  
  4. s less or equal than fraction numerator open parentheses v subscript A end subscript minus v subscript B end subscript close parentheses to the power of 2 end exponent over denominator 2 a end fraction  

The correct answer is: s greater or equal than fraction numerator open parentheses v subscript A end subscript minus v subscript B end subscript close parentheses to the power of 2 end exponent over denominator 2 a end fraction


    For no collision, the speed of car A should be reduced to v subscript B end subscript before the cars meet, i e comma blankfinal relative velocity of car A with respect to car B is zero i e, v subscript r end subscript equals 0
    Here initial relative velocity, u subscript r end subscript equals v subscript A end subscript minus v subscript B end subscript
    Relative acceleration, a subscript r end subscript equals negative a minus 0 equals negative a
    Let relative displacement equals s subscript r end subscript
    The equation
    v subscript r end subscript superscript 2 end superscript equals u subscript r end subscript superscript 2 end superscript plus 2 a subscript r end subscript s subscript r end subscript
    open parentheses 0 close parentheses to the power of 2 end exponent equals open parentheses v subscript A end subscript minus v subscript B end subscript close parentheses minus 2 a s comma
    s subscript r end subscript equals fraction numerator open parentheses v subscript A end subscript minus v subscript B end subscript close parentheses to the power of 2 end exponent over denominator 2 a end fraction
    For no collision, s subscript r end subscript less or equal than s
    i e comma blank fraction numerator open parentheses v subscript A end subscript minus v subscript B end subscript close parentheses to the power of blank over denominator 2 a end fraction less or equal than s

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