the change in kinetic energy is to be equal to the work done.

so to work out the change in kinetic energy we find out the kinetic energy at start and the kinetic energy at the end and then work out the difference between them so:

0.5*m*(30^2-23.5^2) so therefore 170m=140*10^3 J

therefore m = 823.52kg

Oct 16th, 2014

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