1.A train slows down as it rounds a sharp horizontal turn,sl

1.A train slows down as it rounds a sharp horizontal turn,slowing from 90 km/h to 50 km/h in the 15s that it takes to round the bend .the radius of the curve is 150m .compute the acceleration at the moment the train speed reaches 50 km/h.assume it continues to slow down ta this time at the same rate.
2.Figure p3.13 represents the total acceleration of a particle moving clockwise in a circle of radius 2.50 m at a certain time .at this instant,(a)find the radial acceleration,(b)the speed of the particle,and its tangential acceleration.
3.a river hsa a steady speed of 0.500m/s.A student swims upstream a distance of 1.00km and swims back to the 1.20 m/s in still water,how long does the trip take?compare this with the time the trip would take if the water were still.
4.the force (in newtons ) acting on a particle is Fx=(8.00x-16.0),where x is in meters.(a)make a plot of this force versus x from x=0 to x=3.00m.(b)from your graph,find the net work done by this force on the particle as it moves from x=0 to x=3.00m
最好是英文！中文也可以！
发了这么久，难道就没有人会解吗？