A small object with mass mm = 0.0900 kg moves along the +x-axis. The only force on the object is a conservative force that has the potential-energy function U(x)=x²+x³, where = 9.50 J/m² and = 0.300 J/m³. The object is released from rest at small x.

a. When the object is at x = 4.00 m, what is its speed? Express your answer with the appropriate units.

b. When the object is at x = 4.00 m, what is the magnitude of its acceleration? Express your answer with the appropriate units.