Physics 挑戰題

a)As the worker is lowered by one floor below,he loses potential energy
the change in the gravitational potential energy
=(75)(10)(3.5)
=-2625J//
b)The gain in the kinetic energy of each worker is zero,because the platform is lowered uniformly at 0.2m per second ,the velocity of worker remain the same,so there is no gain in kinetic energy
c)from a and b),the worker only loss potential energy but he doesn't gain any kinetic energy.Actually,the loss in potential enrgy should be converted to the increase in kinetic energy,however in partb),the kinetic energy remains the same.Is is the discrepancy

我覺得b題個ke會唔會由0m/s計起..
若是...v=0.2m/s...
K.E.=(1/2)mv^2-(1/2)mu^2
=(1/2)75x0.2^2-0
=1.5J