A five-ton (English ton) car was running on a horizontal highway at a velocity of 60 km/h. And then the driver in the car saw an accident. The diver pressed the brake pedal to make the car full stop. The car skidding on the road to form a mark of 80 m long. Assume that the break force is constant, please calculate the force that applied to the car. The local acceleration of gravity is 9.81 m/s2. The force that applied to the car, F=Answer -8700 N

(a) assume the equation x = at^3 + bt describes the motion of a particular object, with x having the dimension of length and t having the dimension of time. determine the dimensions of the constants a and b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.) (b) determine the dimensions of the derivative dx/dt = 3at^2 + b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.)