20. A cart with mass 450 g moving on a frictionless linear air track at an initial speed of 1.5 m/sundergoes an elastic collision with an initially stationary cart of unknown mass. After the collision,the first cart continues in its original direction at0.70 m/s. What is the mass of the second cart?
(A) 0.16 kg
(B) 0.47 kg
(C) 1.24 kg
(D) 2.14 kg
(E) 3.40 kg