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for this one i did:

convert 45kmh^-1 to ms^-1 which is 12.5ms^-1

my driving force F = -10000 -25000x

change in kinetic energy= 0- (0.5*30000*12.5^2) = -2343750J

\(\int_{0}^{x} -10000 -2500x\)

which gave me expression -10000x - (2500x^2)/2

then -10000x - (2500x^2)/2 = -2343750J

solve by quadratic:

 -10000x - (2500x^2)/2 + 2343750 = 0

which is x=39.48 x=-47.48

My answer should be 78.7M according to the markscheme 

please help thanks

 Mar 31, 2019

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